Circumferential ablation device assembly

ABSTRACT

This invention is a circumferential ablation device assembly which is adapted to forming a circumferential conduction block in a pulmonary vein. The assembly includes a circumferential ablation element which is adapted to ablate a circumferential region of tissue along a pulmonary vein wall which circumscribes the pulmonary vein lumen, thereby transecting the electrical conductivity of the pulmonary vein against conduction along its longitudinal axis and into the left atrium. The circumferential ablation element includes an expandable member with a working length that is adjustable from a radially collapsed position to a radially expanded position. An equatorial band circumscribes the outer surface of the working length and is adapted to ablate tissue adjacent thereto when actuated by an ablation actuator. The equatorial band has a length relative to the longitudinal axis of the expandable member that is narrow relative to the working length, and is also substantially shorter than its circumference when the working length is in the radially expanded position. A pattern of insulators may be included over an ablation element which otherwise spans the working length in order to form the equatorial band described. The expandable member is also adapted to conform to the pulmonary vein in the region of its ostium, such as by providing a great deal of radial compliance or by providing a taper along the working length which has a distally reducing outer diameter. A linear ablation element is provided adjacent to the circumferential ablation element in a combination assembly which is adapted for use in a less-invasive “maze”-type procedure in the region of the pulmonary vein ostia in the left ventricle. A cylindrical ultrasound transducer is provided on an inner member within the balloon and forms the circumferential ablation member by emitting a radial ultrasound signal which is circumferential to the transducer and highly collimated to the transducer&#39;s length. The circumferential ultrasound signal sonically couples to the balloon&#39;s outer skin to form the circumferential ablation element that is adapted to ablate a circumferential path of tissue engaged to the balloon.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/199,736, filed on Nov. 25, 1998, now U.S. Pat. No. 6,117,101 which isa continuation-in-part of U.S. patent application Ser. No. 08/889,798,filed on Jul. 8, 1997, now U.S. Pat. No. 6,024,740, issued Feb. 15,2000, to which this application claims priority under 35 U.S.C. §120.The present application claims the benefit of priority under 35 U.S.C.§119(e) of provisional application Ser. No. 60/073,527, filed on Feb. 3,1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is a surgical device. More specifically, it is acircumferential ablation device assembly which is adapted to ablate aselected circumferential region of tissue which is located either alonga pulmonary vein wall, which forms a circumferential conduction blockagainst conduction along the longitudinal axis of the pulmonary veinwall, or along a left posterior atrial wall which surrounds a pulmonaryvein ostium and electrically isolates the vein and the ostium from therest of the atrium.

2. Description of Related Art

Many abnormal medical conditions in humans and other mammals have beenassociated with disease and other aberrations along the lining or wallswhich define several different body spaces. In order to treat suchabnormal wall conditions of the body spaces, medical device technologiesadapted for delivering specific forms of ablative energy to specificregions of targeted wall tissue from within the associated body spacehave been developed and disclosed.

The terms “body space,” including derivatives thereof, is hereinintended to mean any cavity or lumen within the body which is defined atleast in part by a tissue wall. For example, the cardiac chambers, theuterus, the regions of the gastrointestinal tract, and the arterial orvenous vessels are all considered illustrative examples of body spaceswithin the intended meaning.

The term “lumen,” including derivatives thereof, is herein intended tomean any body space which is circumscribed along a length by a tubulartissue wall and which terminates at each of two ends in at least oneopening that communicates externally of the body space. For example, thelarge and small intestines, the vas deferens, the trachea, and thefallopian tubes are all illustrative examples of lumens within theintended meaning. Blood vessels are also herein considered lumens,including regions of the vascular tree between their branch points. Moreparticularly, the pulmonary veins are lumens within the intendedmeaning, including the region of the pulmonary veins between thebranched portions of their ostia along a left ventricle wall, althoughthe wall tissue defining the ostia typically presents uniquely taperedlumenal shapes.

Atherosclerosis, a vascular disease characterized by abnormal depositsupon vessel walls or thickening thereof, is an example of an abnormalwall condition. The dangers related to flow blockages or functionalocclusions resulting from the disease have made atherosclerosis thefocus of many disclosed devices. Such devices can be categorized bytheir structures and tissue treatment mechanisms. These categories mayinclude direct contact electrode devices, resistance heating devices,light transmission/conversion-to-heat devices, hot fluid lumen devices,and radio frequency (RF) heated devices.

Several direct (or nearly direct) contact electrode devices have beendisclosed. U.S. Pat. No. 4,998,933 to Eggers et al. describes a catheterdesigned for thermal angioplasty which utilizes a heated electrode indirect contact with surrounding tissue or plaque deposits as a mechanismfor treating the diseased lumen walls. U.S. Pat. No. 4,676,258 toInoKuchi et al. and U.S. Pat. No. 4,807,620 to Strul et al. disclosedevices designed to treat surrounding tissues using heat generated bytwo electrodes within the device and an RF power source.

U.S. Pat. No. 4,672,962 to Hershenson and U.S. Pat. No. 5,035,694 toKasprzyk et al. disclose devices which may be categorized as resistanceheating probes. In each of these devices, current flowing through aconductive material at the end of the device provides heat which istransmitted to surrounding tissues for treatment of atherosclerosis andother diseases. Current is transmitted in each of these devices byelectrically conductive materials. In contrast, U.S. Pat. No. 5,226,430to Spears et al. discloses a device which uses light transmitting fiberto transmit energy to a heat generating element at the tip of thedevice. The heat generating element in that device transmits heat energyto a surrounding balloon structure which is in contact with surroundingtissue. In further contrast, U.S. Pat. No. 4,790,311 to Ruiz disclosesan angioplasty catheter system wherein a heat generating electrode atthe tip of the device is heated using the transmission of RF energy.This device may be categorized as an RF heated device.

U.S. Pat. Nos. 5,190,540 and 5,292,321 to Lee can be categorized as hotfluid lumen devices. In the '540 disclosure, Lee describes a ballooncatheter designed for remodelling a body lumen. This device utilizes amultilumen catheter which is capable of delivering heated fluid to anexpandable balloon lumen, thereby expanding the balloon geometricallyand heating tissue which is in contact with the balloon. In the '321disclosure, Lee describes a similar device wherein the lumen of anexpandable balloon is filled with thermoplastic material which isdesigned to become softer and more moldable when heated by a heatingelement.

Endometriosis, another abnormal wall tissue condition, is associatedwith the endometrial cavity of the female. This medical condition,characterized by dangerously proliferative uterine wall tissue along thesurface of the endometrial cavity, has been treated by delivering energyto the tissue. U.S. Pat. No. 5,449,380 to Chin discloses a medicaldevice for delivering energy to the wall tissue of a diseasedendometrial cavity using a balloon lumen with heated fluid circulatingtherein. Other devices, such as those disclosed in U.S. Pat. No.5,505,730 to Edwards; U.S. Pat. No. 5,558,672 to Edwards et al. and U.S.Pat. No. 5,562,720 to Stern et al. are designed for treating particulartissues using heat generated by the flow of RF current betweenelectrodes.

Diseased or structurally damaged blood vessels may bring about variousabnormal wall conditions. The inducement of thrombosis and control ofhemorrhaging within certain body lumens such as vessels have been thefocus of several disclosed devices which use catheter-based heat sourcesfor cauterizing damaged tissues. In U.S. Pat. No. 4,449,528, forexample, Auth et al. disclose a thermal cautery probe designed forheating specific layers of tissue without producing deep tissue damage.The mechanism of heat generation in this device is a resistive coilwithin the cautery probe which is electrically connected to a powersource. In U.S. Pat. No. 4,662,368, Hussein et al. disclose a devicedesigned for localized heat application within a lumen. In this device,energy for heat generation is delivered to the tip of the device in theform of light by a flexible fiber. Heat from an element which convertslight energy to heat energy is then conducted to the adjacent tissue. InU.S. Pat. No. 4,522,205, Taylor et al. disclose a device designed forinducing thrombosis in a blood vessel comprising an array of electrodesmounted onto an expandable balloon which may be delivered by a catheter.The inventors of this device hypothesize that when direct current flowsthrough electrodes which are in contact with adjacent tissues,thrombosis is precipitated.

Maintenance of patency in diseased lumens such as blood vessels has beenthe focus of several disclosed devices, several of which may becharacterized as cardiovascular stents. U.S. Pat. No. 5,078,736 to Behl,for example, discloses an apparatus for maintaining patency in the bodypassages comprising a stent structure which may be connected to aradiofrequency power source. In addition to mechanically supporting abody lumen, this device may provide for thermal disruption of theadjacent tissues which may inhibit reocclusion of the lumen. U.S. Pat.No. 5,178,618 to Kandarpa discloses a similar device which may be usedfor recanalizing an occluded vessel prior to mechanically supporting alumen region.

Atrial Fibrillation

Cardiac arrhythmias, and atrial fibrillation in particular, persist ascommon and dangerous medical ailments, especially in the agingpopulation. In patients with normal sinus rhythm, the heart, which iscomprised of atrial, ventricular, and excitatory conduction tissue, iselectrically excited to beat in a synchronous, patterned fashion. Inpatients with cardiac arrhythmia, abnormal regions of cardiac tissue donot follow the synchronous beating cycle associated with normallyconductive tissue in patients with sinus rhythm. Instead, the abnormalregions of cardiac tissue aberrantly conduct to adjacent tissue, therebydisrupting the cardiac cycle into an asynchronous cardiac rhythm. Suchabnormal conduction has been previously known to occur at variousregions of the heart, such as, for example, in the region of thesino-atrial (SA) node, along the conduction pathways of theatrioventricular (AV) node and the Bundle of His, or in the cardiacmuscle tissue forming the walls of the ventricular and atrial cardiacchambers.

Cardiac arrhythmias, including atrial arrhythmia, may be of amultiwavelet reentrant type, characterized by multiple asynchronousloops of electrical impulses that are scattered about the atrial chamberand are often self propagating. In the alternative or in addition to themultiwavelet reentrant type, cardiac arrhythmias may also have a focalorigin, such as when an isolated region of tissue in an atrium firesautonomously in a rapid, repetitive fashion. Cardiac arrhythmias,including atrial fibrillation, may be generally detected using theglobal technique of an electrocardiogram (EKG). More sensitiveprocedures of mapping the specific conduction along the cardiac chambershave also been disclosed, such as, for example, in U.S. Pat. No.4,641,649 to Walinsky et al. and WO 96/32897 to Desai.

A host of clinical conditions may result from the irregular cardiacfunction and resulting hemodynamic abnormalities associated with atrialfibrillation, including stroke, heart failure, and other thromboembolicevents. In fact, atrial fibrillation is believed to be a significantcause of cerebral stroke, wherein the abnormal hemodynamics in the leftatrium caused by the fibrillatory wall motion precipitate the formationof thrombus within the atrial chamber. A thromboembolism is ultimatelydislodged into the left ventricle, which thereafter pumps the embolisminto the cerebral circulation where a stroke results. Accordingly,numerous procedures for treating atrial arrhythmias have been developed,including pharmacological, surgical, and catheter ablation procedures.

Conventional Atrial Arrhythmia Treatments

Several pharmacological approaches intended to remedy or otherwise treatatrial arrhythmias have been disclosed, such as, for example, in U.S.Pat. No. 4,673,563 to Berne et al.; U.S. Pat. No. 4,569,801 to Molloy etal.; and also by Hindricks, et al. in “Current Management ofArrhythmias” (1991). However, such pharmacological solutions are notgenerally believed to be entirely effective in many cases, and may insome cases result in proarrhythmia and long term inefficacy.

Several surgical approaches have also been developed with the intentionof treating atrial fibrillation. One particular example is known as the“maze procedure,” as is disclosed by Cox, J L et al. in “The surgicaltreatment of atrial fibrillation. I. Summary” Thoracic andCardiovascular Surgery 101(3), pp. 402-405 (1991); and also by Cox, J Lin “The surgical treatment of atrial fibrillation. IV. SurgicalTechnique”, Thoracic and Cardiovascular Surgery 101(4), pp. 584-592(1991). In general, the “maze” procedure is designed to relieve atrialarrhythmia by restoring effective atrial systole and sinus node controlthrough a prescribed pattern of incisions about the tissue wall. In theearly clinical experiences reported, the “maze” procedure includedsurgical incisions in both the right and the left atrial chambers.However, more recent reports predict that the surgical “maze” proceduremay be substantially efficacious when performed only in the left atrium,such as is disclosed in Sueda et al., “Simple Left Atrial Procedure forChronic Atrial Fibrillation Associated With Mitral Valve Disease”(1996).

The “maze procedure” as performed in the left atrium generally includesforming vertical incisions from the two superior pulmonary veins andterminating in the region of the mitral valve annulus, traversing theinferior pulmonary veins en route. An additional horizontal line alsoconnects the superior ends of the two vertical incisions. Thus, theatrial wall region bordered by the pulmonary vein ostia is isolated fromthe other atrial tissue. In this process, the mechanical sectioning ofatrial tissue eliminates the precipitating conduction to the atrialarrhythmia by creating conduction blocks within the aberrant electricalconduction pathways.

While the “maze” procedure as reported by Cox and others, and also othersurgical procedures, have met some success in treating patients withatrial arrhythmia, its highly invasive methodology is believed to beprohibitive in most cases. However, these procedures have provided aguiding principle that mechanically isolating faulty cardiac tissue maysuccessfully prevent atrial arrhythmia, and particularly atrialfibrillation caused by perpetually wandering reentrant wavelets or focalregions of arrhythmogenic conduction.

Modern Catheter Treatments for Atrial Arrhythmia

Success with surgical interventions through atrial segmentation,particularly with regard to the surgical “maze” procedure justdescribed, has inspired the development of less invasive catheter-basedapproaches to treat atrial fibrillation through cardiac tissue ablation.Examples of such catheter-based devices and treatment methods havegenerally targeted atrial segmentation with ablation catheter devicesand methods adapted to form linear or curvilinear lesions in the walltissue which defines the atrial chambers, such as are disclosed in thefollowing U.S. patents: U.S. Pat. No. 5,617,854 to Munsif; U.S. Pat. No.4,898,591 to Jang et al.; U.S. Pat. No. 5,487,385 to Avitall; and U.S.Pat. No. 5,582,609 to Swanson. The disclosures of these patents areherein incorporated in their entirety by reference thereto.

Additional examples of catheter-based tissue ablation in performingless-invasive cardiac chamber segmentation procedures are also disclosedin the following articles: “Physics and Engineering of TranscatheterTissue Ablation”, Avitall et al., Journal of American College ofCardiology, Volume 22, No. 3:921-932 (1993); and “Right and Left AtrialRadiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation,”Haissaguerre, et al., Journal of Cardiovascular Electrophysiology 7(12),pp. 1132-1144 (1996). These articles are herein incorporated in theirentirety by reference thereto.

Furthermore, the use of particular guiding sheath designs for use inablation procedures in both the right and/or left atrial chambers aredisclosed in U.S. Pat. Nos. 5,427,119; 5,497,119; 5,564,440; 5,575,766to Swartz et al. In addition, various energy delivery modalities havebeen disclosed for forming such atrial wall lesions, and include use ofmicrowave, laser, and more commonly, radiofrequency energies to createconduction blocks along the cardiac tissue wall, as disclosed in WO93/20767 to Stern et al.; U.S. Pat. No. 5,104,393 to Isner et al.; andU.S. Pat. No. 5,575,766 to Swartz et al, respectively. The disclosuresof these references are herein incorporated in their entirety byreference thereto.

In addition to attempting atrial wall segmentation with long linearlesions for treating atrial arrhythmia, ablation catheter devices andmethods have also been disclosed which are intended to ablatearrhythmogenic tissue of the left-sided accessory pathways, such asthose associated with the Wolff-Parkinson-White syndrome, through thewall of an adjacent region along the coronary sinus.

For example, Fram et al., in “Feasibility of RF Powered Thermal BalloonAblation of Atrioventricular Bypass Tracts via the Coronary Sinus: Invivo Canine Studies,” PACE, Vol. 18, p 1518-1530 (1995), discloseattempted thermal ablation of left-sided accessory pathways in dogsusing a balloon which is heated with bipolar radiofrequency electrodespositioned within the balloon. A 10 French guiding catheter and a 0.035″wire were provided in an assembly adapted to advance the ablationcatheter into the coronary sinus from the jugular vein. Thermal ablationprocedures were performed in the posterospetal coronary sinus and in theleft free-wall coronary sinus with thermal inflations at either 70 deg,80 deg, or 90 deg for either 30 or 60 seconds. In all cases balloonocclusion was confirmed using distal dye injection. A compliant siliconeballoon was used which had a diameter range of 5-20 mm and a lengthrange of 8-23 mm over a final inflation pressure range of 0.4 to 1.5atms. Fram et al. discloses that the lesion depth of some populationgroups may be sufficient to treat patients with Wolff-Parkinson-Whitesyndrome.

Additional examples of cardiac tissue ablation from the region of thecoronary sinus for the purpose of treating particular types of cardiacarrhythmias are disclosed in: “Long-term effects of percutaneous laserballoon ablation from the canine coronary sinus”, Schuger C D et al.,Circulation (1992) 86:947-954; and “Percutaneous laser ballooncoagulation of accessory pathways”, McMath L P et al., Diagn TherCardiovasc Interven 1991; 1425:165-171.

Focal Arrhythmias Originating from Pulmonary Veins

Atrial fibrillation may be focal in nature, caused by the rapid andrepetitive firing of an isolated center within the atrial cardiac muscletissue. These foci, defined by regions exhibiting a consistent andcentrifugal pattern of electrical activation, may act as either atrigger of atrial fibrillatory paroxysmal or may even sustain thefibrillation. Recent studies have suggested that focal arrhythmia oftenoriginates from a tissue region along the pulmonary veins of the leftatrium, and even more particularly in the superior pulmonary veins.

Less-invasive percutaneous catheter ablation techniques have beendisclosed which use end-electrode catheter designs with the intention ofablating and thereby treating focal arrhythmias in the pulmonary veins.These ablation procedures are typically characterized by the incrementalapplication of electrical energy to the tissue to form focal lesionsdesigned to interrupt the inappropriate conduction pathways.

One example of a focal ablation method intended to destroy and therebytreat focal arrhythmia originating from a pulmonary vein is disclosed byHaissaguerre, et al. in “Right and Left Atrial Radiofrequency CatheterTherapy of Paroxysmal Atrial Fibrillation” in Journal of CardiovascularElectrophysiology 7(12), pp. 1132-1144 (1996). Haissaguerre, et al.disclose radiofrequency catheter ablation of drug-refractory paroxysmalatrial fibrillation using linear atrial lesions complemented by focalablation targeted at arrhythmogenic foci in a screened patientpopulation. The site of the arrhythmogenic foci were generally locatedjust inside the superior pulmonary vein, and were ablated using astandard 4 mm tip single ablation electrode.

In another focal ablation example, Jais et al. in “A focal source ofatrial fibrillation treated by discrete radiofrequency ablation”Circulation 95:572-576 (1997) applies an ablative technique to patientswith paroxysmal arrhythmias originating from a focal source. At the siteof arrhythmogenic tissue, in both right and left atria, several pulsesof a discrete source of radiofrequency energy were applied in order toeliminate the fibrillatory process.

None of the cited references discloses a circumferential ablation deviceassembly which is adapted to form a circumferential conduction blockaround the circumference of a pulmonary vein wall in order to treatfocal left atrial arrhythmias originating in the pulmonary vein.

Nor do the cited references disclose a circumferential ablation devicewith a circumferential ablation element that forms an equatorial bandalong the working length of an expandable element which has a lengththat is substantially less that the working length of the expandableelement.

Nor do the cited references disclose a circumferential ablation devicewith an expandable member which has a shape when expanded that isadapted to conform to a pulmonary vein ostium along a left ventricularwall.

Nor do the cited references disclose a circumferential ablation devicewith an ablation element which circumscribes a radially compliantexpandable element and which is adapted to form a continuouscircumferential lesion in tissue over a working range of expandeddiameters.

Nor do the cited references disclose a circumferential ablation deviceassembly that includes a circumferential ablation element on anexpandable member and also a linear lesion ablation element adjacent tothe expandable member.

Nor do the cited references disclose a circumferential ablation deviceassembly that includes only one a cylindrical ultrasound transducerwhich is positioned within an expandable balloon and which isultrasonically coupled to a circumferential band of the balloon's skinto form an equatorial banded ablation element which is adapted to form acircumferential conduction block along a pulmonary vein.

Nor do the cited references disclose a circumferential ablation deviceassembly which includes a cylindrical ultrasound transducer which ispositioned within an expandable balloon that is adapted, when adjustedto a radially expanded condition, to engage a pulmonary vein such thatthe cylindrical ultrasound transducer is positioned and isultrasonically coupled to a circumferential band of the balloon's skinthat circumscribes the ostium of the vein.

SUMMARY OF THE INVENTION

The present invention is a circumferential ablation device assemblywhich is adapted to form a circumferential lesion along acircumferential path of tissue along a body space wall and whichcircumscribes a body space defined at least in part by the body space.The assembly includes an elongate body, an expandable member on thedistal end portion of the elongate body which is adjustable from aradially collapsed position to a radially expanded position, and acircumferential ablation element that includes an equatorial or othercircumferential band which circumscribes at least a portion of an outersurface of the working length of the expandable member when in theradially expanded position. The circumferential ablation element isadapted to ablate a circumferential region of tissue adjacent to theequatorial band and along the body space wall when the circumferentialablation element is coupled to and actuated by an ablation actuator.

In one variation, the equatorial band length is shorter than two-thirdsthe working length of the expandable member. In one mode of thisvariation, the ablation element includes a circumferential RF electrodein an RF ablation circuit. In another mode, the circumferential ablationelectrode includes a porous membrane along the equatorial or othercircumferential band which is adapted to pass electrically conductivefluid from the conductive fluid chamber and into tissue adjacent to theband, the fluid conducting current to the tissue in an RF ablationcircuit. In still another mode, a thermal conductor is located along theequatorial band and is adapted to emit thermal energy into tissueadjacent to the equatorial band when the thermal conductor is coupled toand actuated by a thermal ablation actuator. In still a further mode, apair of insulators may be positioned exteriorly of each of two ends ofthe circumferential ablation element, wherein the uninsulated spacebetween the insulators forms the equatorial band which may beequatorially located or otherwise circumferentially located.

In another variation of the invention, a circumferential ablation memberincludes an expandable member with a working length which, when adjustedfrom a radially collapsed position to a radially expanded position, isadapted to conform to a pulmonary vein ostium. In one mode of thisvariation, the working length when expanded includes a taper with adistally reducing outer diameter from a proximal region to a distalregion. In a further mode, the expandable member is radially compliantand is adapted to conform to the pulmonary vein ostium when the workinglength is expanded to the radially expanded position in the left atriumand the expandable member is thereafter forced retrogradedly against thepulmonary vein wall in the region of the pulmonary vein ostium.

In another variation of the invention, a circumferential ablation memberincludes an expandable member with a working length which is adjustablebetween a plurality of radially expanded positions each having adifferent expanded outer diameters in the region of the equatorial band.The equatorial band of the circumferential ablation element is adaptedto ablate a continuous circumferential lesion pattern in tissuesurrounding the equatorial band over the range of expanded outerdiameters. In one mode of this variation, the equatorial band has asecondary shape along the outer surface of the working length, such as amodified step, serpentine, or sawtooth shape.

In another variation, the distal end portion of an elongate memberincludes a circumferential ablation member and also a linear ablationmember having an elongate ablation element length and linear ablationelement which is adapted to form a continuous linear lesion in tissueadjacent thereto when the linear ablation element is coupled to anablation actuator. In a further mode of this variation, a first end ofthe linear ablation member is located adjacent to the expandable memberwhich forms at least in part a first anchor adapted to secure the firstlinear ablation member end in the region of a pulmonary vein ostiumalong a left atrium wall. A second anchor is also provided adjacent to asecond, opposite end of the linear ablation member end and is adapted tosecure the second linear ablation member end to a second location alongthe left atrium wall.

In a further mode of the invention, a circumferential ablation deviceassembly includes a cylindrical ultrasound transducer which forms acircumferential ablation member that is adapted to form thecircumferential conduction block. The transducer is positioned within aballoon and is sonically coupled to a circumferential region of theballoon's working length to thereby form a circumferential ablationelement that circumscribes the outer surface of the balloon. Theassembly is adapted to position the circumferential ablation elementadjacent to a circumferential region of tissue along a pulmonary vein inthe region of its ostium, and is further adapted to ablate thatcircumferential region of tissue with ultrasonic energy emitted from thetransducer and coupled to the region of tissue via the circumferentialablation element.

In one aspect of this mode, the balloon is adapted to conform to thepulmonary vein ostium such that the circumferential ablation element isengaged to the circumferential region of tissue. In one variation ofthis aspect, the balloon is highly compliant and is adapted to expand toa radially expanded position which conforms to the pulmonary veinostium. In another variation of this aspect, the balloon has apredetermined shape when expanded to the radially expanded condition andwhich is adapted to conform to the pulmonary vein ostium. Further tothis variation, the predetermined shape may include a distally reducingtapered outer diameter along the working length of the balloon, and maystill further include a pear shape with a contoured region along thattaper.

In another aspect of this mode, only one cylindrical ultrasoundtransducer is provided within the balloon and is adapted to form thecircumferential ablation member.

In another aspect of this mode, the balloon includes a filter which isadapted to adjust either the amount or pattern of the ultrasound energywhich is transmitted to the tissue from the transducer.

In another aspect of this mode, the balloon has a predetermined shapewhich defines at least in part the pattern by which the transducer issonically coupled to the balloon skin to form the circumferentialablation element.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention.

FIGS. 1A-E show schematic, perspective views of various exemplarycircumferential conduction blocks formed in pulmonary vein wall tissuewith the circumferential ablation device assembly of the presentinvention.

FIG. 2 shows a flow diagram of a method for using the circumferentialablation device assembly of the present invention.

FIG. 3 shows a perspective view of a circumferential ablation deviceassembly during use in a left atrium subsequent to performing transeptalaccess and guidewire positioning steps according to the method of FIG.2.

FIG. 4 shows a similar perspective view of the circumferential ablationdevice assembly shown in FIG. 3, and further shows a circumferentialablation catheter during use in ablating a circumferential region oftissue along a pulmonary vein wall to form a circumferential conductionblock in the pulmonary vein according to the method of FIG. 2.

FIG. 5A shows a similar perspective view as shown in FIG. 4, althoughshowing a further circumferential ablation catheter variation which isadapted to allow for blood perfusion from the pulmonary vein and intothe atrium while performing the circumferential ablation method showndiagrammatically in FIG. 2.

FIG. 5B is an enlarged partial view of the circumferential ablationcatheter shown in FIG. 5A, with a perfusion lumen shown in phantom.

FIG. 6 shows a similar perspective view of the left atrium as that shownin FIGS. 3-5, although showing a cross-sectional view of acircumferential lesion after being formed by circumferential catheterablation according to the method of FIG. 2.

FIGS. 7A-B show perspective views of another circumferential ablationcatheter variation during use in a left atrium according to the methodof FIG. 2, wherein FIG. 7A shows a radially compliant expandable memberwith a working length adjusted to a radially expanded position while inthe left atrium, and FIG. 7B shows the expandable member after advancingit into and engaging a pulmonary vein ostium while in the radiallyexpanded position.

FIG. 7C shows the same perspective view of the left atrium shown inFIGS. 7A-B, although shown after forming a circumferential conductionblock according to the circumferential ablation procedure of FIG. 2 andalso after removing the circumferential ablation device assembly fromthe left atrium.

FIG. 8A diagrammatically shows a method for using the circumferentialablation device assembly of the present invention by forming acircumferential conduction block in a pulmonary vein in combination witha method for forming long linear lesions between pulmonary vein ostia ina less-invasive “maze”-type procedure.

FIG. 8B shows a perspective view of a segmented left atrium afterforming several long linear lesions between adjacent pairs of pulmonaryvein ostia according to the method of FIG. 8A.

FIG. 8C shows a similar perspective view as that shown in FIG. 8B,although showing a circumferential ablation device assembly during usein forming a circumferential lesion in a pulmonary vein which intersectswith two linear lesions that extend into the pulmonary vein, accordingto the method of FIG. 8A.

FIG. 8D shows a perspective view of another circumferential ablationcatheter during use according to the method of FIG. 8A, wherein acircumferential ablation member is provided on an elongate catheter bodyadjacent to a linear ablation member such that circumferential andlinear lesions formed in pulmonamy vein wall tissue by the two ablationelements, respectively, intersect.

FIG. 9 diagrammatically shows a further method for using thecircumferential ablation device assembly of the present invention toform a circumferential conduction block in a pulmonary vein wall,wherein signal monitoring and “post-ablation” test elements are used tolocate an arrhythmogenic origin along the pulmonary vein wall and totest the efficacy of a circumferential conduction block in the wall,respectively.

FIGS. 10A-B show perspective views of one circumferential ablationmember variation for use in the circumferential ablation device assemblyof the present invention, showing a circumferential ablation electrodecircumscribing the working length of an expandable member with asecondary shape along the longitudinal axis of the working length whichis a modified step shape, the expandable member being shown in aradially collapsed position and also in a radially expanded position,respectively.

FIGS. 10C-D show perspective views of two circumferential ablationelectrodes which form equatorial or otherwise circumferentially placedbands that circumscribe the working length of an expandable member andthat have serpentine and sawtooth secondary shapes, respectively,relative to the longitudinal axis of the expandable member when adjustedto a radially expanded position.

FIGS. 11A-B show perspective views of another circumferential ablationelement which includes a plurality of individual ablation electrodesthat are spaced circumferentially to form an equatorial band whichcircumscribes the working length of an expandable member either in anequatorial location or an otherwise circumferential location that isbounded both proximally and distally by the working length, and whichare adapted to form a continuous circumferential lesion while theworking length is adjusted to a radially expanded position.

FIG. 12 shows a cross-sectional view of another circumferential ablationmember for use in the circumferential ablation device assembly accordingto the present invention, wherein the circumferential ablation elementcircumscribes an outer surface of an expandable member substantiallyalong its working length and is insulated at both the proximal and thedistal ends of the working length to thereby form an uninsulatedequatorial band in a middle region of the working length or otherwisecircumferential region of the working length which is bounded bothproximally and distally by end portions of the working length, whichmember is adapted to ablate a circumferential path of tissue in apulmonary wall adjacent to the equatorial band.

FIG. 13 shows a perspective view of another circumferential ablationmember which is adapted for use in the circumferential ablation deviceassembly of the present invention, wherein the expandable member isshown to be a cage of coordinating wires which are adapted to beadjusted from a radially collapsed position to a radially expandedposition in order to engage electrode elements on the wires about acircumferential pattern of tissue in a pulmonary vein wall.

FIG. 14 shows a cross-sectional view of another circumferential ablationelement which is adapted for use in the circumferential ablation deviceassembly of the present invention. A superelastic, looped electrodeelement is shown at the distal end of a pusher and is adapted tocircumferentially engage pulmonary vein wall tissue to form acircumferential lesion as a conduction block that circumscribes thepulmonary vein lumen.

FIG. 15A shows a longitudinal cross-sectional view of anothercircumferential ablation catheter according to the present invention,and shows the ablation element to include a single cylindricalultrasound transducer which is positioned along an inner member withinan expandable balloon which is further shown in a radially expandedcondition.

FIG. 15B shows a transverse cross-sectional view of the circumferentialablation catheter shown in FIG. 15A taken along line 15B—15B shown inFIG. 15A.

FIG. 15C shows a transverse cross-sectional view of the circuferentialablation catheter shown in FIG. 15A taken along line 15C—15C shown inFIG. 15A.

FIG. 15D shows a perspective view of the ultrasonic transducer of FIG.15A in isolation.

FIG. 15E shows a modified version of the ultrasonic transducer of FIG.15D with individually driven sectors.

FIG. 16A shows a perspective view of a similar circumferential ablationcatheter to the catheter shown in FIG. 15, and shows the distal endportion of the circumferential ablation catheter during one mode of usein forming a circumferential conduction block in a pulmonary vein in theregion of its ostium along a left atrial wall (shown in cross-section inshadow).

FIG. 16B shows a similar perspective and cross-section shadow view of acircumferential ablation catheter and pulmonary vein ostium as thatshown in FIG. 16A, although shows another circumferential ablationcatheter wherein the balloon has a tapered outer diameter.

FIG. 16C shows a similar view to that shown in FIGS. 16A-B, althoughshowing another circumferential ablation catheter wherein the balloonhas a “pear”-shaped outer diameter with a contoured surface along ataper which is adapted to seat in the ostium of a pulmonary vein.

FIG. 16D shows a cross-sectional view of one circumferential conductionblock which may be formed by use of a circumferential ablation cathetersuch as that shown in FIG. 16C.

FIG. 17A shows a cross-sectional view of the distal end portion ofanother circumferential ablation catheter according to the presentinvention, wherein an outer shield or filter is provided along theballoon's outer surface in order to form a predetermined shape for thecircumferential ablation element created by sonic transmissions from theinner ultrasound transducer.

FIG. 17B shows a similar view as that shown in FIG. 17A, althoughshowing the distal end portion of another circumferential ablationcatheter which includes a heat sink as an equatorial band within thecircumferential path of energy emission from an inner ultrasoundtransducer.

FIG. 18A shows a transverse cross-sectional view of an additionalcircumferential ablation catheter according to the present invention,and shows the ablation element to include a single transducer sectorsegment which is positioned along an inner member within an expandableballoon which is further shown in a radially expanded condition.

FIG. 18B shows a transverse cross-sectional view of an a furthercircumferential ablation catheter according to the present invention,and shows the ablation element to include a single curvilinear sectionthat is mounted so as to position its concave surface facing in aradially outward direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As will be described with reference to the detailed embodiments below,the present invention is a circumferential ablation device assemblywhich is adapted to treat patients with atrial arrhythmia by forming acircumferential conduction block in a pulmonary vein which blockselectrical conduction along the longitudinal axis of the pulmonary veinwall and into the left atrium.

The terms “circumference” or “circumferential”, including derivativesthereof, are herein intended to mean a continuous path or line whichforms an outer border or perimeter that surrounds and thereby defines anenclosed region of space. Such a continuous path starts at one locationalong the outer border or perimeter, and translates along the outerborder or perimeter until it is completed at the original startinglocation to enclose the defined region of space. The related term“circumscribe,” including derivatives thereof, is herein intended tomean to enclose, surround, or encompass a defined region of space.Therefore, according to these defined terms, a continuous line which istraced around a region of space and which starts and ends at the samelocation “circumscribes” the region of space and has a “circumference”which is defined by the distance the line travels as it translates alongthe path circumscribing the space.

Still further, a circumferential path or element may include one or moreof several shapes, and may be, for example, circular, oblong, ovular,elliptical, or otherwise planar enclosures. A circumferential path mayalso be three dimensional, such as, for example, two opposite-facingsemi-circular paths in two different parallel or off-axis planes whichare connected at their ends by line segments bridging between theplanes.

For purpose of further illustration, FIGS. 1A-D therefore show variouscircumferential paths A, B, C, and D, respectively, each translatingalong a portion of a pulmonary vein wall and circumscribing a definedregion of space, shown at a, b, c, and d also respectively, eachcircumscribed region of space being a portion of a pulmonary vein lumen.For still further illustration of the three-dimensional circumferentialcase shown in FIG. 1D, FIG. 1E shows an exploded perspective view ofcircumferential path D as it circumscribes multiplanar portions of thepulmonary vein lumen shown at d′, d″, and d′″, which together make upregion d as shown in FIG. 1D.

The term “transect”, including derivatives thereof, is also hereinintended to mean to divide or separate a region of space into isolatedregions. Thus, each of the regions circumscribed by the circumferentialpaths shown in FIGS. 1A-D transects the respective pulmonary vein,including its lumen and its wall, to the extent that the respectivepulmonary vein is divided into a first longitudinal region located onone side of the transecting region, shown, for example, at region “X” inFIG. 1A, and a second longitudinal region on the other side of thetransecting plane, shown, for example, at region “Y” also in FIG. 1A.

Therefore, a “circumferential conduction block” according to the presentinvention is formed along a region of tissue which follows acircumferential path along the pulmonary vein wall, circumscribing thepulmonary vein lumen and transecting the pulmonary vein relative toelectrical conduction along its longitudinal axis. The transectingcircumferential conduction block therefore isolates electricalconduction between opposite longitudinal portions of the pulmonary wallrelative to the conduction block and along the longitudinal axis.

The terms “ablate” or “ablation,” including derivatives thereof, arehereafter intended to mean the substantial altering of the mechanical,electrical, chemical, or other structural nature of tissue. In thecontext of intracardiac ablation applications shown and described withreference to the variations of the illustrative embodiment below,“ablation” is intended to mean sufficient altering of tissue propertiesto substantially block conduction of electrical signals from or throughthe ablated cardiac tissue.

The term “element” within the context of “ablation element” is hereinintended to mean a discrete element, such as an electrode, or aplurality of discrete elements, such as a plurality of spacedelectrodes, which are positioned so as to collectively ablate a regionof tissue.

Therefore, an “ablation element” according to the defined terms mayinclude a variety of specific structures adapted to ablate a definedregion of tissue. For example, one suitable ablation element for use inthe present invention may be formed, according to the teachings of theembodiments below, from an “energy emitting” type which is adapted toemit energy sufficient to ablate tissue when coupled to and energized byan energy source. Suitable “energy emitting” ablation elements for usein the present invention may therefore include, for example: anelectrode element adapted to couple to a direct current (“DC”) oralternating current (“AC”) current source, such as a radiofrequency(“RF”) current source; an antenna element which is energized by amicrowave energy source; a heating element, such as a metallic elementor other thermal conductor which is energized to emit heat such as byconvective or conductive heat transfer, by resistive heating due tocurrent flow, or by optical heating with light; a light emittingelement, such as a fiber optic element which transmits light sufficientto ablate tissue when coupled to a light source or an ultrasonic elementsuch as an ultrasound crystal element which is adapted to emitultrasonic sound waves sufficient to ablate tissue when coupled to asuitable excitation source.

In addition, other elements for altering the nature of tissue may besuitable as “ablation elements” under the present invention when adaptedaccording to the detailed description of the invention below. Forexample, a cryoblation element adapted to sufficiently cool tissue tosubstantially alter the structure thereof may be suitable if adaptedaccording to the teachings of the current invention. Furthermore, afluid delivery element, such as a discrete port or a plurality of portswhich are fluidly coupled to a fluid delivery source, may be adapted toinfuse an ablating fluid, such as a fluid containing alcohol, into thetissue adjacent to the port or ports to substantially alter the natureof that tissue.

The term “diagnose”, including derivatives thereof, is intended toinclude patients suspected or predicted to have atrial arrhythmia, inaddition to those having specific symptoms or mapped electricalconduction indicative of atrial arrhythmia.

In one aspect of using the circumferential ablation device assembly ofthe present invention, a patient diagnosed with multiple waveletarrhythmia originating from multiple regions along the atrial wall istreated in part by forming the circumferential conduction block as anadjunct to forming long linear regions of conduction block betweenadjacent pulmonary vein ostia in a less-invasive “maze”-type catheterablation procedure. More detail regarding particular ablation catheterembodiments adapted for use in such a method is provided below withreference to a combination circumferential-long linear lesion ablationdevice which is described below with reference to FIGS. 8A-D.

A patient diagnosed with focal arrhythmia originating from anarrhythmogenic origin or focus in a pulmonary vein may also be treatedwith the circumferential ablation device assembly of the presentinvention by using the assembly to form a circumferential conductionblock along a circumferential path of pulmonary vein wall tissue thateither includes the arrhythmogenic origin or is between the origin andthe left atrium. In the former case, the arrhythmogenic tissue at theorigin is destroyed by the conduction block as it is formed through thatfocus. In the latter case, the arrhythmogenic focus may still conductabnormally, although such aberrant conduction is prevented from enteringand affecting the atrial wall tissue due to the interveningcircumferential conduction block.

FIG. 2 diagrammatically shows the sequential steps of a method for usingthe circumferential ablation device assembly of the present invention informing a circumferential conduction block in a pulmonary vein. Thecircumferential ablation method according to FIG. 2 includes:positioning a circumferential ablation element at an ablation regionalong the pulmonary vein according to a series of detailed steps showncollectively in FIG. 2 as positioning step (3); and thereafter ablatinga continuous circumferential region of tissue in the PV wall at theablation region according to ablation step (4).

Further to positioning step (3) according to the method of FIG. 2, adistal tip of a guiding catheter is first positioned within the leftatrium according to a transeptal access method, which is furtherdescribed in more detail as follows. The right venous system is firstaccessed using the “Seldinger” technique, wherein a peripheral vein(such as a femoral vein) is punctured with a needle, the puncture woundis dilated with a dilator to a size sufficient to accommodate anintroducer sheath, and an introducer sheath with at least one hemostaticvalve is seated within the dilated puncture wound while maintainingrelative hemostasis. With the introducer sheath in place, the guidingcatheter or sheath is introduced through the hemostatic valve of theintroducer sheath and is advanced along the peripheral vein, into theregion of the vena cavae, and into the right atrium.

Once in the right atrium, the distal tip of the guiding catheter ispositioned against the fossa ovalis in the intraatrial septal wall. A“Brochenbrough” needle or trocar is then advanced distally through theguide catheter until it punctures the fossa ovalis. A separate dilatormay also be advanced with the needle through the fossa ovalis to preparean access port through the septum for seating the guiding catheter. Theguiding catheter thereafter replaces the needle across the septum and isseated in the left atrium through the fossa ovalis, thereby providingaccess for object devices through its own inner lumen and into the leftatrium.

It is however further contemplated that other left atrial access methodsmay be suitable substitutes for using the circumferential ablationdevice assembly of the present invention. In one alternative variationnot shown, a “retrograde” approach may be used, wherein the guidingcatheter is advanced into the left atrium from the arterial system. Inthis variation, the Seldinger technique is employed to gain vascularaccess into the arterial system, rather than the venous, for example, ata femoral artery. The guiding catheter is advanced retrogradedly throughthe aorta, around the aortic arch, into the ventricle, and then into theleft atrium through the mitral valve.

Subsequent to gaining transeptal access to the left atrium as justdescribed, positioning step (3) according to FIG. 2 next includesadvancing a guidewire into a pulmonary vein, which is done generallythrough the guiding catheter seated in the fossa ovalis. In addition tothe left atrial access guiding catheter, the guidewire according to thisvariation may also be advanced into the pulmonary vein by directing itinto the vein with a second sub-selective delivery catheter (not shown)which is coaxial within the guiding catheter, such as, for example, byusing one of the directional catheters disclosed in U.S. Pat. No.5,575,766 to Swartz. Or, the guidewire may have sufficient stiffness andmaneuverability in the left atrial cavity to unitarily subselect thedesired pulmonary vein distally of the guiding catheter seated at thefossa ovalis.

Suitable guidewire designs for use in the overall circumferentialablation device assembly of the present invention may be selected frompreviously known designs, while generally any suitable choice shouldinclude a shaped, radiopaque distal end portion with a relatively stiff,torquable proximal portion adapted to steer the shaped tip under X-rayvisualization. Guidewires having an outer diameter ranging from 0.010″to 0.035″ may be suitable. In cases where the guidewire is used tobridge the atrium from the guiding catheter at the fossa ovalis, andwhere no other sub-selective guiding catheters are used, guidewireshaving an outer diameter ranging from 0.018″ to 0.035″ may be required.It is believed that guidewires within this size range may be required toprovide sufficient stiffness and maneuverability in order to allow forguidewire control and to prevent undesirable guidewire prolapsing withinthe relatively open atrial cavity.

Subsequent to gaining pulmonary vein access, positioning step (3) ofFIG. 2 next includes tracking the distal end portion of acircumferential ablation device assembly over the guidewire and into thepulmonary vein, followed by positioning a circumferential ablationelement at an ablation region of the pulmonary vein where thecircumferential conduction block is to be desirably formed.

FIGS. 3-4 further show a circumferential ablation device assembly (100)according to the present invention during use in performing positioningstep (3) and ablation step (4) just described with reference to FIG. 2.Included in the circumferential ablation device assembly (100) areguiding catheter (101), guidewire (102), and circumferential ablationcatheter (103).

More specifically, FIG. 3 shows guiding catheter (101) subsequent toperforming a transeptal access method according to FIG. 2, and alsoshows guidewire (102) subsequent to advancement and positioning within apulmonary vein, also according to step (3) of FIG. 2. FIG. 3 showscircumferential ablation catheter (103) as it tracks coaxially overguidewire (102) with a distal guidewire tracking member, which isspecifically shown only in part at first and second distal guidewireports (142,144) located on the distal end portion (132) of an elongatecatheter body (130). A guidewire lumen (not shown) extends between thefirst and second distal guidewire ports (142,144) and is adapted toslideably receive and track over the guidewire. In the particularvariation of FIG. 3, the second distal guidewire port (142) is locatedon a distal end portion (132) of the elongate catheter body (130),although proximally of first distal guidewire port (142).

As would be apparent to one of ordinary skill, the distal guidewiretracking member shown in FIG. 3 and just described may be slideablycoupled to the guidewire externally of the body in a “backloading”technique after the guidewire is first positioned in the pulmonary vein.Furthermore, there is no need in this guidewire tracking variation for aguidewire lumen in the proximal portions of the elongate catheter body(130), which allows for a reduction in the outer diameter of thecatheter shaft in that region. Nevertheless, it is further contemplatedthat a design which places the second distal guidewire port on theproximal end portion of the elongate catheter body would also beacceptable, as is described below, for example, with reference to theperfusion embodiment of FIG. 5.

In addition, the inclusion of a guidewire lumen extending within theelongate body between first and second ports, as provided in FIG. 3,should not limit the scope of acceptable guidewire tracking membersaccording to the present invention. Other guidewire tracking memberswhich form a bore adapted to slideably receive and track over aguidewire are also considered acceptable, such as, for example, thestructure adapted to engage a guidewire as described in U.S. Pat. No.5,505,702 to Arney, the entirety of which is hereby incorporated byreference herein.

While the assemblies and methods shown variously throughout the Figuresinclude a guidewire coupled to a guidewire tracking member on thecircumferential ablation catheter, other detailed variations may also besuitable for positioning the circumferential ablation element at theablation region in order to form a circumferential conduction blockthere. For example, an alternative circumferential ablation catheter notshown may include a “fixed-wire”-type of design wherein a guidewire isintegrated into the ablation catheter as one unit. In anotheralternative assembly, the same type of sub-selective sheaths describedabove with reference to U.S. Pat. No. 5,575,766 to Swartz for advancinga guidewire into a pulmonary vein may also be used for advancing acircumferential ablation catheter device across the atrium and into apulmonary vein.

FIG. 3 also shows circumferential ablation catheter (103) with acircumferential ablation element (160) formed on an expandable member(170). The expandable member (170) is shown in FIG. 3 in a radiallycollapsed position adapted for percutaneous translumenal delivery intothe pulmonary vein according to positioning step (3) of FIG. 2. However,expandable member (170) is also adjustable to a radially expandedposition when actuated by an expansion actuator (175), as shown in FIG.4. Expansion actuator (175) may include, but is not limited to, apressurizeable fluid source. According to the expanded state shown inFIG. 4, expandable member (170) includes a working length L relative tothe longitudinal axis of the elongate catheter body which has a largerexpanded outer diameter OD than when in the radially collapsed position.Furthermore, the expanded outer diameter OD is sufficient tocircumferentially engage the ablation region of the pulmonary vein.Therefore, the terms “working length” are herein intended to mean thelength of an expandable member which, when in a radially expandedposition, has an expanded outer diameter that is: (a) greater than theouter diameter of the expandable member when in a radially collapsedposition; and (b) sufficient to engage a body space wall or adjacentablation region surrounding the expandable member, at least on twoopposing internal sides of the body space wall or adjacent ablationregion, with sufficient surface area to anchor the expandable member.

Circumferential ablation element (160) also includes a circumferentialband (152) on the outer surface of working length L which is coupled toan ablation actuator (190) at a proximal end portion of the elongatecatheter body (shown schematically). After expandable member (170) isadjusted to the radially expanded position and at least a portion ofworking length L circumferentially engages the pulmonary vein wall inthe ablation region, the circumferential band (152) of thecircumferential ablation element (160) is actuated by ablation actuator(190) to ablate the surrounding circumferential path of tissue in thepulmonary vein wall, thereby forming a circumferential lesion thatcircumscribes the pulmonary vein lumen and transects the electricalconductivity of the pulmonary vein to block conduction in a directionalong its longitudinal axis.

FIG. 5A shows another circumferential ablation catheter (203) during usealso according to the method of FIG. 2, wherein a perfusion lumen (260)(shown in phantom in FIG. 5B) is formed within the distal end portion(232) of elongate catheter body (230). The perfusion lumen (260) in thisexample is formed between a distal perfusion port, which in this exampleis the first distal guidewire port (242), and proximal perfusion port(244). Proximal perfusion port (244) is formed through the wall of theelongate catheter body (230) and communicates with the guidewire lumen(not shown) which also forms the perfusion lumen between the distal andproximal perfusion ports. In the particular design shown, after theguidewire has provided for the placement of the ablation element intothe pulmonary vein, the guidewire is withdrawn proximally of theproximal perfusion port (244) (shown schematically in shadow) so thatthe lumen between the ports is clear for antegrade blood flow into thedistal perfusion port (242), proximally along the perfusion lumen, outthe proximal perfusion port (244) and into the atrium (perfusion flowshown schematically with arrows).

Further to the perfusion design shown in FIGS. 5A-B, guidewire (102) ispositioned in a guidewire lumen which extends the entire length of theelongate catheter body (230) in an “over-the-wire”-type of design, whichfacilitates the proximal withdrawal of the guidewire to allow forperfusion while maintaining the ability to subsequently readvance theguidewire distally through the first distal guidewire port (242) forcatheter repositioning. In one alternative variation not shown, theguidewire is simply withdrawn and disengaged from the second distalguidewire port (244), in which case the circumferential ablationcatheter must generally be withdrawn from the body in order to recouplethe distal guidewire tracking member with the guidewire.

In another alternative perfusion variation not shown which is amodification of the embodiment of FIG. 5A, a proximal perfusion port isprovided as a separate and distinct port positioned between the seconddistal guidewire port (244) and the expandable member (270), whichallows for proximal withdrawal of the guidewire to clear the guidewirelumen and thereby form a perfusion lumen between the first distalguidewire port and the proximal perfusion port. The guidewire of thisalternative variation, however, remains engaged within the guidewirelumen between the second distal guidewire port and the proximalperfusion port.

Passive perfusion during expansion of the expandable member is believedto minimize stasis and allow the target pulmonary vein to continue inits atrial filling function during the atrial arrhythmia treatmentprocedure. Without this perfusion feature, the expandable member when inthe radially expanded position during ablation blocks the flow from thevein into the atrium, which flow stasis may result in undesirablethrombogenesis in the pulmonary vein distally to the expandable member.In addition, in cases where the ablation element is adapted to ablatetissue with heat conduction at the ablation region, as described byreference to more detailed embodiments below, the perfusion featureaccording to the variation of FIGS. 5A-B may also provide a coolingfunction in the surrounding region, including in the blood adjacent tothe expandable member.

Moreover, in addition to the specific perfusion structure shown anddescribed by reference to FIGS. 5A-B, it is to be further understoodthat other structural variants which allow for perfusion flow duringexpansion of the expandable element may provide suitable substitutesaccording to one of ordinary skill without departing from the scope ofthe present invention.

FIG. 6 shows pulmonary vein (52) after removing the circumferentialablation device assembly subsequent to forming a circumferential lesion(70) around the ablation region of the pulmonary vein wall (53)according to the use of the circumferential ablation device assemblyshown in stepwise fashion in FIGS. 3-6. Circumferential lesion (70) isshown located along the pulmonary vein adjacent to the pulmonary veinostium (54), and is shown to also be “transmural,” which is hereinintended to mean extending completely through the wall, from one side tothe other. Also, the circumferential lesion (70) is shown in FIG. 6 toform a “continuous” circumferential band, which is herein intended tomean without gaps around the pulmonary vein wall circumference, therebycircumscribing the pulmonary vein lumen.

It is believed, however, that circumferential catheter ablation with acircumferential ablation element according to the present invention mayleave some tissue, either transmurally or along the circumference of thelesion, which is not actually ablated, but which is not substantialenough to allow for the passage of conductive signals. Therefore, theterms “transmural” and “continuous” as just defined are intended to havefunctional limitations, wherein some tissue in the ablation region maybe unablated but there are no functional gaps which allow forsymptomatically arrhythmogenic signals to conduct through the conductionblock and into the atrium from the pulmonary vein.

Moreover, it is believed that the functionally transmural and continuouslesion qualities just described are characteristic of a completedcircumferential conduction block in the pulmonary vein. Such acircumferential conduction block thereby transects the vein, isolatingconduction between the portion of the vein on one longitudinal side ofthe lesion and the portion on the other side. Therefore, any foci oforiginating arrhythmogenic conduction which is opposite the conductionblock from the atrium is prevented by the conduction block fromconducting down into the atrium and atrial arrhythmic affects aretherefore nullified.

FIGS. 7A-B show a further variation of the present invention, wherein acircumferential ablation member (350) includes a radially compliantexpandable member (370) which is adapted to conform to a pulmonary veinostium (54) at least in part by adjusting it to a radially expandedposition while in the left atrium and then advancing it into the ostium.FIG. 7A shows expandable member (370) after being adjusted to a radiallyexpanded position while located in the left atrium (50). FIG. 7B furthershows expandable member (370) after being advanced into the pulmonaryvein (52) until at least a portion of the expanded working length L ofcircumferential ablation member (350), which includes a circumferentialband (352), engages the pulmonary vein ostium (54). FIG. 7C shows aportion of a circumferential lesion (72) which forms a circumferentialconduction block in the region of the pulmonary vein ostium (54)subsequent to actuating the circumferential ablation element to form thecircumferential lesion.

FIGS. 8A-D collectively show a circumferential ablation device assemblyaccording to the present invention as it is used to form acircumferential conduction block adjunctively to the formation of longlinear lesions in a less-invasive “maze”-type procedure, as introducedabove for the treatment of multiwavelet reentrant type fibrillationalong the left atrial wall.

More specifically, FIG. 8A diagrammatically shows a summary of steps forperforming a “maze”-type procedure by forming circumferential conductionblocks that intersect with long linear conduction blocks formed betweenthe pulmonary veins. As disclosed in copending patentapplication(Application Number not yet assigned) entitled “TissueAblation Device and Method of Use” filed by Michael Lesh, M.D. on May 9,1997, which is herein incorporated in its entirety by reference thereto,a box-like conduction block surrounding an arrhythmogenic atrial wallregion bounded by the pulmonary veins may be created by forming longlinear lesions between anchors in all pairs of adjacent pulmonary veinostia, such as is shown in part in steps (5) and (6) of FIG. 8A.However, it is further believed that, in some particular applications,such linear lesions may be made sufficiently narrow with respect to thesurface area of the pulmonary vein ostia that they may not intersect,thereby leaving gaps between them which may present proarrhythmicpathways for abnormal conduction into and from the box, such as is shownbetween linear lesions (57,58) in FIG. 8B. Therefore, by forming thecircumferential conduction block according to step (7) of FIG. 8A, andas shown by use of circumferential ablation member (450) in FIG. 8C, thelinear lesions are thereby bridged and the gaps are closed.

In a further variation to the specific embodiments shown in FIGS. 8B-C,FIG. 8D shows a circumferential ablation device assembly which includesboth circumferential and linear ablation elements (452,460),respetively. Circumferential ablation member (450) is shown to includean expandable member (470) which is adjusted to a radially expandposition that is asymmetric to the underlying catheter shaft. Linearablation member (460) extends along the elongate body proximally fromthe circumferential ablation member (450). When expanded sufficiently toengage the pulmonary vein wall, expandable member (470) provides atleast a portion of an anchor for a first end (462) of linear ablationmember (460).

A shaped stylet (466) is shown in shadow in FIG. 8D within the elongatecatheter body in the region of the second end (464) of the linearablation member (460). Shaped stylet (466) includes a port or opening(465) though which guidewire (469) passes in order to anchor the secondend (464) into an adjacent pulmonary vein ostium such that the linearablation member (460) is adapted to substantially contact the leftatrial wall between the adjacent vein ostia to form the linear ablationaccording to the method of FIG. 8A. Alternatively to the use of shapedstylet (466) and guidewire (469), it is further contemplated that asecond anchor may effected with, for example, an intermediate guidewiretracking member adapted to track over a guidewire (469) engaged to thepulmonary vein.

FIG. 9 diagrammatically shows a further method for using thecircumferential ablation device assembly of the present inventionwherein electrical signals along the pulmonary vein are monitored with asensing element before and after ablation according to steps (8) and(9), respectively. Signals within the pulmonary vein are monitored priorto forming a conduction block, as indicated in step (8) in FIG. 9, inorder to confirm that the pulmonary vein chosen contains anarrhythmogenic origin for atrial arrhythmia. Failure to confirm anarrhythmogenic origin in the pulmonary vein, particularly in the case ofa patient diagnosed with focal arrhythmia, may dictate the need tomonitor signals in another pulmonary vein in order to direct treatmentto the proper location in the heart. In addition, monitoring thepre-ablation signals may be used to indicate the location of thearrhythmogenic origin of the atrial arrhythmia, which information helpsdetermine the best location to form the conduction block. As such, theconduction block may be positioned to include and therefore ablate theactual focal origin of the arrhythmia, or may be positioned between thefocus and the atrium in order to block aberrant conduction from thefocal origin and into the atrial wall.

In addition or in the alternative to monitoring electrical conductionsignals in the pulmonary vein prior to ablation, electrical signalsalong the pulmonary vein wall may also be monitored by the sensingelement subsequent to circumferential ablation, according to step (9) ofthe method of FIG. 9. This monitoring method aids in testing theefficacy of the ablation in forming a complete conduction block againstarrhythmogenic conduction. Arrhythmogenic firing from the identifiedfocus will not be observed during signal monitoring along the pulmonaryvein wall when taken below a continuous circumferential and transmurallesion formation, and thus would characterize a successfulcircumferential conduction block. In contrast, observation of sucharrhythmogenic signals between the lesion and the atrial wallcharacterizes a functionally incomplete or discontinuous circumference(gaps) or depth (transmurality) which would potentially identify theneed for a subsequent follow-up procedure, such as a secondcircumferential lesioning procedure in the ablation region.

A test electrode may also be used in a “post ablation” signal monitoringmethod according to step (10) of FIG. 9. In one particular embodimentnot shown, the test electrode is positioned on the distal end portion ofan elongate catheter body and is electrically coupled to a currentsource for firing a test signal into the tissue surrounding the testelectrode when it is placed distally or “upstream” of thecircumferential lesion in an attempt to simulate a focal arrhythmia.This test signal generally challenges the robustness of thecircumferential lesion in preventing atrial arrhythmia from any suchfuture physiologically generated aberrant activity along the suspectvein.

Further to the signal monitoring and test stimulus methods justdescribed, such methods may be performed with a separate electrode orelectrode pair located on the catheter distal end portion adjacent tothe region of the circumferential ablation element, or may be performedusing one or more electrodes which form the circumferential ablationelement itself, as will be further developed below.

Circumferential Ablation Member

The designs for the expandable member and circumferential ablationelement for use in the circumferential ablation device assembly of thepresent invention have been described generically with reference to theembodiments shown in the previous Figures. Examples of more specificexpandable member and ablation element embodiments which are adapted foruse in the assembly of the present invention are further provided asfollows.

Notwithstanding their somewhat schematic detail, the circumferentialablation members shown in the previous figures do illustrate oneparticular embodiment wherein a circumferential electrode elementcircumscribes an outer surface of an expandable member. The expandablemember of the embodiments shown may take one of several different forms,although the expandable member is generally herein shown as aninflatable balloon that is coupled to an expansion actuator (175) whichis a pressurizeable fluid source. The balloon is preferably made of apolymeric material and forms a fluid chamber which communicates with afluid passageway (not shown in the figures) that extends proximallyalong the elongate catheter body and terminates proximally in a proximalfluid port that is adapted to couple to the pressurizeable fluid source.

In one expandable balloon variation, the balloon is constructed of arelatively inelastic polymer such as a polyethylene (“PE”; preferablylinear low density or high density or blends thereof), polyolefincopolymer (“POC”), polyethylene terepthalate (“PET”), polyimide, or anylon material. In this construction, the balloon has a low radial yieldor compliance over a working range of pressures and may be folded into apredetermined configuration when deflated in order to facilitateintroduction of the balloon into the desired ablation location via knownpercutaneous catheterization techniques. In this variation, one balloonsize may not suitably engage all pulmonary vein walls for performing thecircumferential ablation methods of the present invention on all needypatients. Therefore, it is further contemplated that a kit of multipleablation catheters, with each balloon working length having a uniquepredetermined expanded diameter, may be provided from which a treatingphysician may chose a particular device to meet a particular patient'spulmonary vein anatomy.

In an alternative expandable balloon variation, the balloon isconstructed of a relatively compliant, elastomeric material, such as,for example (but not limited to), a silicone, latex, or mylar elastomer.In this construction, the balloon takes the form of a tubular member inthe deflated, non-expanded state. When the elastic tubular balloon ispressurized with fluid such as in the previous, relatively non-compliantexample, the material forming the wall of the tubular member elasticallydeforms and stretches radially to a predetermined diameter for a giveninflation pressure. It is further contemplated that the compliantballoon may be constructed as a composite, such as, for example, a latexor silicone balloon skin which includes fibers, such as metal, Kevlar,or nylon fibers, which are embedded into the skin. Such fibers, whenprovided in a predetermined pattern such as a mesh or braid, may providea controlled compliance along a preferred axis, preferably limitinglongitudinal compliance of the expandable member while allowing forradial compliance.

It is believed that, among other features, the relatively compliantvariation may provide a wide range of working diameters, which may allowfor a wide variety of patients, or of vessels within a single patient,to be treated with just one or a few devices. Furthermore, this range ofdiameters is achievable over a relatively low range of pressures, whichis believed to diminish a potentially traumatic vessel response that mayotherwise be presented concomitant with higher pressure inflations,particularly when the inflated balloon is oversized to the vessel. Inaddition, the low-pressure inflation feature of this variation issuitable for the present invention because the functional requirement ofthe expandable balloon is merely to engage the ablation element againsta circumferential path along the inner lining of the pulmonary veinwall.

Moreover, a circumferential ablation member is adapted to conform to thegeometry of the pulmonary vein ostium, at least in part by providingsubstantial compliance to the expandable member, as was shown anddescribed previously by reference to FIGS. 7A-B. Further to thisconformability to pulmonary vein ostium as provided in the specificdesign of FIGS. 7A-B, the working length L of expandable member (370) isalso shown to include a taper which has a distally reducing outerdiameter from a proximal end (372) to a distal end (374). In either acompliant or the non-compliant balloon, such a distally reducing taperedgeometry adapts the circumferential ablation element to conform to thefunneling geometry of the pulmonary veins in the region of their ostiain order to facilitate the formation of a circumferential conductionblock there.

Further to the circumferential electrode element embodiment as shownvariously throughout the previous illustrative Figures, thecircumferential electrode element is coupled to an ablation actuator(190). Ablation actuator (190) generally includes a radio-frequency(“RF”) current source (not shown) that is coupled to both the RFelectrode element and also a ground patch (195) which is in skin contactwith the patient to complete an RF circuit. In addition, ablationactuator (190) preferably includes a monitoring circuit (not shown) anda control circuit (not shown) which together use either the electricalparameters of the RF circuit or tissue parameters such as temperature ina feedback control loop to drive current through the electrode elementduring ablation. Also, where a plurality of ablation elements orelectrodes in one ablation element are used, a switching means may beused to multiplex the RF current source between the various elements orelectrodes.

FIGS. 10A-D show various patterns of electrically conductive,circumferential electrode bands as electrode ablation elements, eachcircumscribing an outer surface of the working length of an expandablemember. FIGS. 10A-B show circumferential ablation member (550) toinclude a continuous circumferential electrode band (552) thatcircumscribes an outer surface of an expandable member (570). FIG. 10Bmore specifically shows expandable member (570) as a balloon which isfluidly coupled to a pressurizeable fluid source (175), and furthershows electrode band (circumferential ablation element) (552)electrically coupled via electrically conductive lead (554) to ablationactuator (190). In addition, a plurality of apertures (572) are shown inthe balloon skin wall of expandable member (570) adjacent to electrodeband (552). The purpose of these apertures (572) is to provide apositive flow of fluid such as saline or ringers lactate fluid into thetissue surrounding the electrode band (552). Such fluid flow is believedto reduce the temperature rise in the tissue surrounding the electrodeelement during RF ablation.

The shapes shown collectively in FIGS. 10A-D allow for a continuouselectrode band to circumscribe an expandable member's working lengthover a range of expanded diameters, a feature which is believed to beparticularly useful with a relatively compliant balloon as theexpandable member. In the particular embodiments of FIGS. 10A-D, thisfeature is provided primarily by a secondary shape given to theelectrode band relative to the longitudinal axis of the working lengthof the expandable member. Electrode band (552) is thus shown in FIGS.10A-B to take the specific secondary shape of a modified step curve.Other shapes than a modified step curve are also suitable, such as theserpentine or sawtooth secondary shapes shown respectively in FIGS.10C-D. Other shapes in addition to those shown in FIGS. 10A-D and whichmeet the defined functional requirements are further contemplated withinthe scope of the present invention.

In addition, the electrode band provided by the circumferential ablationelements shown in FIGS. 10C-D and also shown schematically in FIGS. 3-5has a functional band width w relative to the longitudinal axis of theworking length which is only required to be sufficiently wide to form acomplete conduction block against conduction along the walls of thepulmonary vein in directions parallel to the longitudinal axis. Incontrast, the working length L of the respective expandable element isadapted to securely anchor the distal end portion in place such that theablation element is firmly positioned at a selected region of thepulmonary vein for ablation. Accordingly, the band width w is relativelynarrow compared to the working length L of the expandable element, andthe electrode band may thus form a relatively narrow equatorial bandwhich has a band width that is less than two-thirds or even one-half ofthe working length of the expandable element. Additionally, it is to benoted here and elsewhere throughout the specification, that a narrowband may be placed at locations other than the equator of the expandableelement, preferably as long as the band is bordered on both sides by aportion of the working length L.

In another aspect of the narrow equatorial band variation for thecircumferential ablation element, the circumferential lesion formed mayalso be relatively narrow when compared to its own circumference, andmay be less than two-thirds or even one-half its own circumference onthe expandable element when expanded. In one arrangement which isbelieved to be suitable for ablating circumferential lesions in thepulmonary veins as conduction blocks, the band width w is less than 1 cmwith a circumference on the working length when expanded that is greaterthan 1.5 cm.

FIGS. 11A-B show a further variation of a circumferential ablationelement which is adapted to maintain a continuous circumferential lesionpattern over a range of expanded diameters and which includes electrodeelements that form a relatively narrow equatorial band around theworking length of an expandable balloon member. In this variation, aplurality of individual electrode/ablation elements (562) are includedin the circumferential ablation element and are positioned in spacedarrangement along an equatorial band which circumscribes an outersurface of the expandable member's working length L.

The size and spacing between these individual electrode elements (562),when the balloon is expanded, is adapted to form a substantiallycontinuous circumferential lesion in pulmonary vein wall tissue when inintimal contact adjacent thereto, and is further adapted to form such alesion over a range of band diameters as the working length is adjustedbetween a variety of radially expanded positions. Each individualelectrode element (562) has two opposite ends (563,564), respectively,along a long axis LA and also has a short axis SA, and is positionedsuch that the long axis LA is at an acute angle relative to thelongitudinal axis La of the elongate catheter body and expandable member(560). At least one of the ends (563,564) along the long axis LAoverlaps with an end of another adjacent individual electrode element,such that there is a region of overlap along their circumferentialaspect, i.e., there is a region of overlap along the circumferentialcoordinates. The terms “region of overlap along their circumferentialcoordinate” are herein intended to mean that the two adjacent ends eachare positioned along the working length with a circumferential and alsoa longitudinal coordinate, wherein they share a common circumferentialcoordinate. In this arrangement, the circumferential compliance alongthe working length which accompanies radial expansion of the expandablemember also moves the individual electrode elements apart along thecircumferential axis. However, the spaced, overlapping arrangementdescribed allows the individual ablation elements to maintain a certaindegree of their circumferential overlap, or at least remain close enoughtogether, such that a continuous lesion may be formed without gapsbetween the elements.

The construction for suitable circumferential electrode elements in theRF variation of the present invention, such as the various electrodeembodiments described with reference to FIGS. 10A-12B, may comprise ametallic material deposited on the outer surface of the working lengthusing conventional techniques, such as by plasma depositing, sputtercoating, chemical vapor deposition, other known techniques which areequivalent for this purpose, or otherwise affixing a metallic shapedmember onto the outer surface of the expandable member such as throughknown adhesive bonding techniques. Other RF electrode arrangements arealso considered within the scope of the present invention, so long asthey form a circumferential conduction block as previously described.For example, a balloon skin may itself be metallized, such as by mixingconductive metal, including but not limited to gold, platinum, orsilver, with a polymer to form a compounded, conductive matrix as theballoon skin.

Still further to the RF electrode embodiments, another circumferentialablation member variation (not shown) may also include an expandablemember, such as an inflatable balloon, that includes a porous skin thatis adapted to allow fluid, such as hypertonic saline solution, to passfrom an internal chamber defined by the skin and outwardly intosurrounding tissues. Such a porous skin may be constructed according toseveral different methods, such as by forming holes in an otherwisecontiguous polymeric material, including mechanically drilling or usinglaser energy, or the porous skin may simply be an inherently porousmembrane. In any case, by electrically coupling the fluid within theporous balloon skin to an RF current source (preferably monopolar), theporous region of the expandable member serves as an RF electrode whereinRF current flows outwardly through the pores via the conductive fluid.In addition, it is further contemplated that a porous outer skin may beprovided externally of another, separate expandable member, such as aseparate expandable balloon, wherein the conductive fluid is containedin a region between the porous outer skin and the expandable membercontained therein. Various other “fluid electrode” designs than thosespecifically herein described may also be suitable according to one ofordinary skill upon review of this disclosure.

In the alternative, or in addition to the RF electrode variations justdescribed, the circumferential ablation element may also include otherablative energy sources or sinks, and particularly may include a thermalconductor that circumscribes the outer circumference of the workinglength of an expandable member. Examples of suitable thermal conductorarrangements include a metallic element which may, for example, beconstructed as previously described for the more detailed RF embodimentsabove. However, in the thermal conductor embodiment such a metallicelement would be generally either resistively heated in a closed loopcircuit internal to the catheter, or conductively heated by a heatsource coupled to the thermal conductor. In the latter case ofconductive heating of the thermal conductor with a heat source, theexpandable member may be, for example, a polymeric balloon skin which isinflated with a fluid that is heated either by a resistive coil or bybipolar RF current. In any case, it is believed that a thermal conductoron the outer surface of the expandable member is suitable when it isadapted to heat tissue adjacent thereto to a temperature between 40 degand 80 deg Celsius.

Further to the thermal conduction variation for the circumferentialablation element, the perfusion balloon embodiment as shown in FIGS.5A-B may be particularly useful in such a design. It is believed thatablation through increased temperatures, as provided by example abovemay also enhance coagulation of blood in the pulmonay vein adjacent tothe expandable member, which blood would otherwise remain stagnantwithout such a perfusion feature.

One further circumferential ablation element design which is believed tobe highly useful in performing the methods according to the presentinvention is shown in FIG. 12 to include a circumferential ablationmember(600) with two insulators (602,604) that encapsulate the proximaland distal ends, respectively, of the working length L of an expandablemember (610). In the particular embodiment shown, the insulators(602,604) are thermal insulators, such as a thermal insulator comprisinga Teflon material. Expandable member (610) is an inflatable balloonwhich has a balloon skin (612) that is thermally conductive tosurrounding tissue when inflated with a heated fluid which may contain aradiopaque agent, saline fluid, ringers lactate, combinations thereof,other known biocompatible fluids having acceptable heat transferproperties for these purposes, further to the thermal conductorembodiments previously described. By providing these spaced insulators,a circumferential ablation element is formed as an equatorial band (603)of uninsulated balloon skin is located between the opposite insulators.In this configuration, the circumferential ablation element is able toconduct heat externally of the balloon skin much more efficiently at theuninsulated equatorial band (603) than at the insulated portions, andthereby is adapted to ablate only a circumferential region of tissue ina pulmonary vein wall which is adjacent to the equatorial band. It isfurther noted that this embodiment is not limited to an “equatorial”placement of the ablation element. Rather, a circumferential band may beformed anywhere along the working length of the expandable member andcircumscribing the longitudinal axis of the expandable member aspreviously described.

FIG. 12 further shows use of a radiopaque marker (620) to identify thelocation of the equatorial band (603) in order to facilitate placementof that band at a selected ablation region of a pulmonary vein via X-rayvisualization. Radiopaque marker (620) is opaque under X-ray, and may beconstructed, for example, of a radiopaque metal such as gold, platinum,or tungsten, or may comprise a radiopaque polymer such as a metal loadedpolymer. FIG. 12 shows radiopaque marker (620) positioned coaxially overan inner tubular member (621) which is included in a coaxial catheterdesign as would be apparent to one of ordinary skill. The presentinvention contemplates the combination of such a radiopaque markeradditionally in the other embodiments herein shown and described. Tonote, when the circumferential ablation member which forms an equatorialband includes a metallic electrode element, such electrode may itself beradiopaque and may not require use of a separate marker as justdescribed.

The thermal insulator embodiment just described by reference to FIG. 12is illustrative of a broader embodiment, wherein a circumferentialablation member has an ablating surface along the entire working lengthof an expandable member, but is shielded from releasing ablative energyinto surrounding tissues except for along an unshielded or uninsulatedequatorial band. As such, the insulator embodiment contemplates otherablation elements, such as the RF embodiments previously describedabove, which are provided along the entire working length of anexpandable member and which are insulated at their ends to selectivelyablate tissue only about an uninsulated equatorial band.

In a further example using the insulator embodiment in combination witha circumferential RF electrode embodiment, a metallized balloon whichincludes a conductive balloon skin may have an electrical insulator,such as a polymeric coating, at each end of the working length andthereby selectively ablate tissue with electricity flowing through theuninsulated equatorial band. In this and other insulator embodiments, itis further contemplated that the insulators described may be onlypartial and still provide the equatorial band result. For instance, inthe conductive RF electrode balloon case, a partial electrical insulatorwill allow a substantial component of current to flow through theuninsulated portion due to a “shorting” response to the lower resistancein that region.

In still a further example of an insulator combined with an RF ablationelectrode, a porous membrane comprises the entire balloon skin of anexpandable member. By insulating the proximal and distal end portions ofthe working length of the expandable member, only the pores in theunexposed equatorial band region are allowed to effuse the electrolytewhich carries an ablative RF current.

Further to the expandable member design for use in a circumferentialablation element according to the present invention, other expandablemembers than a balloon are also considered suitable. For example, in oneexpandable cage embodiment shown in FIG. 13, cage (650) comprisescoordinating wires (651) and is expandable to engage a desired ablationregion in a pulmonary vein.

The radial expansion of cage (650) is accomplished as follows. Sheath(652) is secured around the wires proximally of cage (650). However,core (653), which may be a metallic mandrel such as stainless steel,extends through sheath (652) and distally within cage (650) wherein itterminates in a distal tip (656). Wires (651) are secured to distal tip(656), for example, by soldering, welding, adhesive bonding, heatshrinking a polymeric member over the wires, or any combination of thesemethods. Core (653) is slideable within sheath (652), and may, forexample, be housed within a tubular lumen (not shown) within sheath(652), the wires being housed between a coaxial space between thetubular lumen and sheath (652). By moving the sheath (652) relative tocore (653) and distal tip (656)(shown by arrows in FIG. 13), the cage(650) is collapsible along its longitudinal axis in order to force anoutward radial bias (also shown with arrows in FIG. 13) to wires (651)in an organized fashion to formed a working length of cage (650) whichis expanded (not shown).

Further to the particular expandable cage embodiment shown in FIG. 13, aplurality of ablation electrodes (655) is shown, each being positionedon one of wires (651) and being similarly located along the longitudinalaxis of the cage (650). The radial bias given to wires (651) duringexpansion, together with the location of the ablation electrodes (655),serves to position the plurality of ablation electrodes/elements (655)along a circumferential, equatorial band along the expanded workinglength of cage (650). The wires forming a cage according to thisembodiment may also have another predetermined shape when in theradially expanded position. For example, a taper similar to that shownfor expandable member (370) in FIGS. 7A-B may be formed by expandingcage (650), wherein the ablation element formed by ablation electrodes(655) may be positioned between the proximal end and the distal end ofthe taper.

Further to the construction of the embodiment shown in FIG. 13, wires(651) are preferably metal, and may comprise stainless steel or asuperelastic metal alloy, such as an alloy of nickel and titanium, or acombination of both. Regarding the case of nickel and titaniumconstruction for wires (655), a separate electrical conductor may berequired in order to actuate ablation electrodes (655) to efficientlyemit ablative current into surrounding tissues. In the case where wires(651) are constructed of stainless steel, they may also serve aselectrical conductors for ablation electrodes (655). Further to thestainless steel design, the wires (651) may be coated with an electricalinsulator to isolate the electrical flow into surrounding tissues at thesite of the ablation electrodes (655). Moreover, the ablation electrodes(655) in the stainless steel wire variation may be formed simply byremoving electrical insulation in an isolated region to allow forcurrent to flow into tissue only from that exposed region.

In a further cage embodiment (not shown) to that shown in FIG. 13, acircumferential strip of electrodes may also be secured to the cage(650) such that the strip circumscribes the cage at a predeterminedlocation along the cage's longitudinal axis. By expanding cage (650) aspreviously described, the strip of electrodes are adapted to take acircumferential shape according to the shape of the expanded cage (650).Such an electrode strip is preferably flexible, such that it may beeasily reconfigured when the cage is adjusted between the radiallycollapsed and expanded positions and such that the strip may be easilyadvanced and withdrawn with the cage within the delivery sheath.Furthermore, the electrode strip may be a continuous circumferentialelectrode such as a conductive spring coil, or may be a flexible stripwhich includes several separate electrodes along its circumferentiallength. In the latter case, the flexible strip may electrically coupleall of the electrodes to a conductive lead that interfaces with a drivecircuit, or each electrode may be separately coupled to one or more suchconductive leads.

Another circumferential ablation element adapted for use in thecircumferential conduction block assembly according to the presentinvention is shown in FIG. 14, wherein circumferential ablation member(700) includes a looped member (710) attached, preferably by heatshrinking, to a distal end of a pusher (730). Looped member (710) andpusher (730) are slideably engaged within delivery sheath (750) suchthat looped member (710) is in a first collapsed position whenpositioned and radially confined within delivery sheath (750), andexpands to a second expanded position when advanced distally fromdelivery sheath (750).

Looped member (710) is shown in more detail in FIG. 14 to include a core(712) which is constructed of a superelastic metal alloy such as anickel-titanium alloy and which has a looped portion with shape memoryin the looped configuration. This looped configuration is shown in FIG.14 to be in a plane which is off-axis, preferably perpendicular, to thelongitudinal axis of the pusher (730). This off-axis orientation of theloop is adapted to engage a circumferential path of tissue along apulmonary vein wall which circumscribes the pulmonary vein lumen whenthe looped member (710) is delivered from the delivery sheath (750) whenthe delivery sheath is positioned within the vein lumen parallel to itslongitudinal axis. An ablation electrode (714) is also shown in FIG. 14as a metallic coil which is wrapped around core (712) in its loopedportion.

Pusher (730) is further shown in FIG. 14 to include a tubular pushermember (732) which is heat shrunk over two ends (712′) of core (712)which extend proximally of looped member (710) through pusher (730) inthe particular variation shown. While in this embodiment core (712)extends through the pusher in order to provide stiffness to thecomposite design for the pusher, it is further contemplated that thesuperelastic metal of the core may be replaced or augmented in thepusher region with another different mandrel or pusher core (not shown),such as a stiffer stainless steel mandrel. Also shown within pusher(730) is an electrically conductive lead (735) which is coupled to theablation electrode (714) and which is also adapted in a proximal regionof the pusher (not shown) to couple to an ablation actuator (190) suchas an RF current source (shown schematically).

Ultrasound Circumferential Ablation Member

FIGS. 15A-18B show various specific embodiments of a broadercircumferential ablation device assembly which utilizes an ultrasonicenergy source to ablate tissue. The present circumferential ablationdevice has particular utility in connection with forming acircumferential lesion within or about a pulmonary vein ostium or withinthe vein itself in order to form a circumferential conductive block.This application of the present ablation device, however, is merelyexemplary, and it is understood that those skilled in the art canreadily adapt the present ablation device for applications in other bodyspaces.

As common to each of the following embodiments, a source of acousticenergy is provided a delivery device that also includes an anchoringmechanism. In one mode, the anchoring device comprises an expandablemember that also positions the acoustic energy source within the body;however, other anchoring and positioning devices may also be used, suchas, for example, a baket mechanism. In a more specific form, theacoustic energy source is located within the expandable member and theexpandable member is adapted to engage a circumferential path of tissueeither about or along a pulmonary vein in the region of its ostium alonga left atrial wall. The acoustic energy source in turn is acousticallycoupled to the wall of the expandable member and thus to thecircumferential region of tissue engaged by the expandable member wallby emitting a circumferential and longitudinally collimated ultrasoundsignal when actuated by an acoustic energy driver. The use of acousticenergy, and particularly ultrasonic energy, offers the advantage ofsimultaneously applying a dose of energy sufficient to ablate arelatively large surface area within or near the heart to a desiredheating depth without exposing the heart to a large amount of current.For example, a collimated ultrasonic transducer can form a lesion, whichhas about a 1.5 mm width, about a 2.5 mm diameter lumen, such as apulmonary vein and of a sufficient depth to form an effective conductiveblock. It is believed that an effective conductive block can be formedby producing a lesion within the tissue that is transmural orsubstantially transmural. Depending upon the patient as well as thelocation within the pulmonary vein ostium, the lesion may have a depthof 1 millimeter to 10 millimeters. It has been observed that thecollimated ultrasonic transducer can be powered to provide a lesionhaving these parameters so as to form an effective conductive blockbetween the pulmonary vein and the posterior wall of the left atrium.

With specific reference now to the embodiment illustrated in FIGS. 15Athrough 15D, a circumferential ablation device assembly (800) includesan elongate body (802) with proximal and distal end portions (810,812),an expandable balloon (820) located along the distal end portion (812)of elongate body (802), and a circumferential ultrasound transducer(830) which forms a circumferential ablation member which isacoustically coupled to the expandable balloon (820). In more detail,FIGS. 15A-C variously show elongate body (802) to include guidewirelumen (804), inflation lumen (806), and electrical lead lumen (808). Theablation device, however, can be of a self steering type rather than anover-the-wire type device.

Each lumen extends between a proximal port (not shown) and a respectivedistal port, which distal ports are shown as distal guidewire port (805)for guidewire lumen (804), distal inflation port (807) for inflationlumen (806), and distal lead port (809) for electrical lead lumen (808).Although the guidewire, inflation and electrical lead lumens aregenerally arranged in a side-by-side relationship, the elongate body(802) can be constructed with one or more of these lumens arranged in acoaxial relationship, or in any of a wide variety of configurations thatwill be readily apparent to one of ordinary skill in the art.

In addition, the elongate body (802) is also shown in FIGS. 15A and 15Cto include an inner member (803) which extends distally beyond distalinflation and lead ports (807,809), through an interior chamber formedby the expandable balloon (820), and distally beyond expandable balloon(820) where the elongate body terminates in a distal tip. The innermember (803) forms the distal region for the guidewire lumen (804)beyond the inflation and lead ports, and also provides a support memberfor the cylindrical ultrasound transducer (830) and for the distal neckof the expansion balloon, as described in more detail below.

One more detailed construction for the components of the elongate body(802) which is believed to be suitable for use in transeptal left atrialablation procedures is as follows. The elongate body (802) itself mayhave an outer diameter provided within the range of from about 5 Frenchto about 10 French, and more preferable from about 7 French to about 9French. The guidewire lumen preferably is adapted to slideably receiveguidewires ranging from about 0.010 inch to about 0.038 inch indiameter, and preferably is adapted for use with guidewires ranging fromabout 0.018 inch to about 0.035 inch in diameter. Where a 0.035 inchguidewire is to be used, the guidewire lumen preferably has an innerdiameter of 0.040 inch to about 0.042 inch. In addition, the inflationlumen preferably has an inner diameter of about 0.020 inch in order toallow for rapid deflation times, although may vary based upon theviscosity of inflation medium used, length of the lumen, and otherdynamic factors relating to fluid flow and pressure.

In addition to providing the requisite lumens and support members forthe ultrasound transducer assembly, the elongate body (802) of thepresent embodiment must also be adapted to be introduced into the leftatrium such that the distal end portion with balloon and transducer maybe placed within the pulmonary vein ostium in a percutaneoustranslumenal procedure, and even more preferably in a transeptalprocedure as otherwise herein provided. Therefore, the distal endportion (812) is preferably flexible and adapted to track over and alonga guidewire seated within the targeted pulmonary vein. In one furthermore detailed construction which is believed to be suitable, theproximal end portion is adapted to be at least 30% more stiff than thedistal end portion. According to this relationship, the proximal endportion may be suitably adapted to provide push transmission to thedistal end portion while the distal end portion is suitably adapted totrack through bending anatomy during in vivo delivery of the distal endportion of the device into the desired ablation region.

Notwithstanding the specific device constructions just described, otherdelivery mechanisms for delivering the ultrasound ablation member to thedesired ablation region are also contemplated. For example, while theFIG. 15A variation is shown as an “over-the-wire” catheter construction,other guidewire tracking designs may be suitable substitutes, such as,for example, catheter devices which are known as “rapid exchange” or“monorail” variations wherein the guidewire is only housed coaxiallywithin a lumen of the catheter in the distal regions of the catheter. Inanother example, a deflectable tip design may also be a suitablesubstitute and which is adapted to independently select a desiredpulmonary vein and direct the transducer assembly into the desiredlocation for ablation. Further to this latter variation, the guidewirelumen and guidewire of the FIG. 15A variation may be replaced with a“pullwire” lumen and associated fixed pullwire which is adapted todeflect the catheter tip by applying tension along varied stiffnesstransitions along the catheter's length. Still further to this pullwirevariation, acceptable pullwires may have a diameter within the rangefrom about 0.008 inch to about 0.020 inch, and may further include ataper, such as, for example, a tapered outer diameter from about 0.020inch to about 0.008 inch.

More specifically regarding expandable balloon (820) as shown in varieddetail between FIGS. 15A and 15C, a central region (822) is generallycoaxially disposed over the inner member (803) and is bordered at itsend neck regions by proximal and distal adaptions (824,826). Theproximal adaption (824) is sealed over elongate body (802) proximally ofthe distal inflation and the electrical lead ports (807,809), and thedistal adaption (826) is sealed over inner member (803). According tothis arrangement, a fluid tight interior chamber is formed withinexpandable balloon (820). This interior chamber is fluidly coupled to apressurizeable fluid source (not shown) via inflation lumen (806). Inaddition to the inflation lumen (806), electrical lead lumen (808) alsocommunicates with the interior chamber of expandable balloon (820) sothat the ultrasound transducer (830), which is positioned within thatchamber and over the inner member (803), may be electrically coupled toan ultrasound drive source or actuator, as will be provided in moredetail below.

The expandable balloon (820) may be constructed from a variety of knownmaterials, although the balloon (820) preferably is adapted to conformto the contour of a pulmonary vein ostium. For this purpose, the balloonmaterial can be of the highly compliant variety, such that the materialelongates upon application of pressure and takes on the shape of thebody lumen or space when fully inflated. suitable balloon materialsinclude elastomers, such as, for example, but without limitation,Silicone, latex, or low durometer polyurethane (for example, a durometerof about 80A).

In addition or in the alternative to constructing the balloon of highlycompliant material, the balloon (820) can be formed to have a predefinedfully inflated shape (i.e., be preshaped) to generally match theanatomic shape of the body lumen in which the balloon is inflated. Forinstance, as described below in greater detail, the balloon can have adistally tapering shape to generally match the shape of a pulmonary veinostium, and/or can include a bulbous proximal end to generally match atransition region of the atrium posterior wall adjacent to the pulmonaryvein ostium. In this manner, the desired seating within the irregulargeometry of a pulmonary vein or vein ostium can be achieved with bothcompliant and non-compliant balloon variations.

Notwithstanding the alternatives which may be acceptable as justdescribed, the balloon (820) is preferably constructed to exhibit atleast 300% expansion at 3 atmospheres of pressure, and more preferablyto exhibit at least 400% expansion at that pressure. The term“expansion” is herein intended to mean the balloon outer diameter afterpressurization divided by the balloon inner diameter beforepressurization, wherein the balloon inner diameter before pressurizationis taken after the balloon is substantially filled with fluid in ataught configuration. In other words, “expansion” is herein intended torelate to change in diameter that is attributable to the materialcompliance in a stress strain relationship. In one more detailedconstruction which is believed to be suitable for use in most conductionblock procedures in the region of the pulmonary veins, the balloon isadapted to expand under a normal range of pressure such that its outerdiameter may be adjusted from a radially collapsed position of about 5millimeters to a radially expanded position of about 2.5 centimeters (orapproximately 500% expansion ratio).

The ablation member, which is illustrated in FIGS. 15A-D, takes the formof annular ultrasonic transducer (830). In the illustrated embodiment,the annular ultrasonic transducer (830) has a unitary cylindrical shapewith a hollow interior (i.e., is tubular shaped); however, thetransducer applicator (830) can have a generally annular shape and beformed of a plurality of segments. For instance, the transducerapplicator (830) can be formed by a plurality of tube sectors thattogether form an annular shape. The tube sectors can also be ofsufficient arc lengths so as when joined together, the sectors assemblyforms a “clover-leaf” shape. This shape is believed to provide overlapin heated regions between adjacent elements. The generally annular shapecan also be formed by a plurality of planar transducer segments whichare arranged in a polygon shape (e.g., hexagon). In addition, althoughin the illustrated embodiment the ultrasonic transducer comprises asingle transducer element, the transducer applicator can be formed of amulti-element array, as described in greater detail below.

As is shown in detail in FIG. 15D, cylindrical ultrasound transducer(830) includes a tubular wall (831) which includes three concentrictubular layers. The central layer (832) is a tubular shaped member of apiezoceramic or piezoelectric crystalline material. The transducerpreferably is made of type PZT-4, PZT-5 or PZT-8, quartz orLithium-Niobate type piezoceramic material to ensure high power outputcapabilities. These types of transducer materials are commerciallyavailable from Stavely Sensors, Inc. of East Hartford, Conn., or fromValpey-Fischer Corp. of Hopkinton, Mass.

The outer and inner tubular members (833,834) enclose central layer(832) within their coaxial space and are constructed of an electricallyconductive material. In the illustrated embodiment, these transducerelectrodes (833, 834) comprise a metallic coating, and more preferably acoating of nickel, copper, silver, gold, platinum, or alloys of thesemetals.

One more detailed construction for a cylindrical ultrasound transducerfor use in the present application is as follows. The length of thetransducer (830) or transducer assembly (e.g., multi-element array oftransducer elements) desirably is selected for a given clinicalapplication. In connection with forming circumferential condition blocksin cardiac or pulmonary vein wall tissue, the transducer length can fallwithin the range of approximately 2 mm up to greater than 10 mm, andpreferably equals about 5 mm to 10 mm. A transducer accordingly sized isbelieved to form a lesion of a width sufficient to ensure the integrityof the formed conductive block without undue tissue ablation. For otherapplications, however, the length can be significantly longer.

Likewise, the transducer outer diameter desirably is selected to accountfor delivery through a particular access path (e.g., percutaneously andtranseptally), for proper placement and location within a particularbody space, and for achieving a desired ablation effect. In the givenapplication within or proximate of the pulmonary vein ostium, thetransducer (830) preferably has an outer diameter within the range ofabout 1.8 mm to greater than 2.5 mm. It has been observed that atransducer with an outer diameter of about 2 mm generates acoustic powerlevels approaching 20 Watts per centimeter radiator or greater withinmyocardial or vascular tissue, which is believed to be sufficient forablation of tissue engaged by the outer balloon for up to about 2 cmouter diameter of the balloon. For applications in other body spaces,the transducer applicator (830) may have an outer diameter within therange of about 1 mm to greater than 3-4 mm (e.g., as large as 1 to 2 cmfor applications in some body spaces).

The central layer (832) of the transducer (830) has a thickness selectedto produce a desired operating frequency. The operating frequency willvary of course depending upon clinical needs, such as the tolerableouter diameter of the ablation and the depth of heating, as well as uponthe size of the transducer as limited by the delivery path and the sizeof the target site. As described in greater detail below, the transducer(830) in the illustrated application preferably operates within therange of about 5 MHz to about 20 MHz, and more preferably within therange of about 7 MHz to about 10 MHz. Thus, for example, the transducercan have a thickness of approximately 0.3 mm for an operating frequencyof about 7 MHz (i.e., a thickness generally equal to ½ the wavelengthassociated with the desired operating frequency).

The transducer (830) is vibrated across the wall thickness and toradiate collimated acoustic energy in the radial direction. For thispurpose, as best seen in FIGS. 15A and 15D, the distal ends ofelectrical leads (836,837) are electrically coupled to outer and innertubular members or electrodes (833,834), respectively, of the transducer(830), such as, for example, by soldering the leads to the metalliccoatings or by resistance welding. In the illustrated embodiment, theelectrical leads are 4-8 mil (0.004 to 0.008 inch diameter) silver wireor the like.

The proximal ends of these leads are adapted to couple to an ultrasonicdriver or actuator (840), which is schematically illustrated in FIG.15D. FIGS. 15A-D further show leads (836,837) as separate wires withinelectrical lead lumen (808), in which configuration the leads must bewell insulated when in close contact. Other configurations for leads(836,837) are therefore contemplated. For example, a coaxial cable mayprovide one cable for both leads which is well insulated as toinductance interference. Or, the leads may be communicated toward thedistal end portion (812) of the elongate body through different lumenswhich are separated by the catheter body.

The transducer also can be sectored by scoring or notching the outertransducer electrode (833) and part of the central layer (832) alonglines parallel to the longitudinal axis L of the transducer (830), asillustrated in FIG. 15E. A separate electrical lead connects to eachsector in order to couple the sector to a dedicated power control thatindividually excites the corresponding transducer sector. By controllingthe driving power and operating frequency to each individual sector, theultrasonic driver (840) can enhance the uniformity of the ultrasonicbeam around the transducer (830), as well as can vary the degree ofheating (i.e., lesion control) in the angular dimension.

The ultrasound transducer just described is combined with the overalldevice assembly according to the present embodiment as follows. Inassembly, the transducer (830) desirably is “air-backed” to produce moreenergy and to enhance energy distribution uniformity, as known in theart. In other words, the inner member (803) does not contact anappreciable amount of the inner surface of transducer inner tubularmember (834). This is because the piezoelectric crystal which formscentral layer (832) of ultrasound transducer (830) is adapted toradially contract and expand (or radially “vibrate”) when an alternatingcurrent is applied from a current source and across the outer and innertubular electrodes (833,834) of the crystal via the electrical leads(836,837). This controlled vibration emits the ultrasonic energy whichis adapted to ablate tissue and form a circumferential conduction blockaccording to the present embodiment. Therefore, it is believed thatappreciable levels of contact along the surface of the crystal mayprovide a dampening effect which would diminish the vibration of thecrystal and thus limit the efficiency of ultrasound transmission.

For this purpose, the transducer (830) seats coaxial about the innermember (803) and is supported about the inner member (803) in a mannerproviding a gap between the inner member (803) and the transducer innertubular member (834). That is, the inner tubular member (834) forms aninterior bore (835) which loosely receives the inner member (803). Anyof a variety of structures can be used to support the transducer (830)about the inner member (803). For instance, spaces or splines can beused to coaxially position the transducer (830) about the inner member(803) while leaving a generally annular space between these components.In the alternative, other conventional and known approaches to supportthe transducer can also be used. For instance, O-rings that circumscribethe inner member (803) and lie between the inner member (803) and thetransducer (830) can support the transducer (830) in a manner similar tothat illustrated in U.S. Pat. No. 5,606,974, issued Mar. 4, 1997, andentitled “Catheter Having Ultrasonic Device.” More detailed examples ofthe alternative transducer support structures just described arerespectfully disclosed in the following references: U.S. Pat. No.5,620,479 to Diederich, issued Apr. 15, 1997, and entitled “Method andApparatus for Thermal Therapy of Tumors,” and U.S. Pat. No. 5,606,974 toCastellano, issued Mar. 4, 1997, and entitled “Catheter HavingUltrasonic Device.” The disclosures of these references are hereinincorporated in their entirety by reference thereto.

In the illustrated embodiment, a stand-off (838) is provided in order toensure that the transducer (830) has a radial separation from the innermember (803) to form a gap filled with air and/or other fluid. In onepreferred mode shown in FIG. 15D, stand-off (838) is a tubular memberwith a plurality of circumferentially spaced outer splines (839) whichhold the majority of the transducer inner surface away from the surfaceof the stand-off between the splines, thereby minimizing dampeningaffects from the coupling of the transducer to the catheter. The tubularmember which forms a stand-off such as stand-off (838) in the FIG. 15Dembodiment may also provide its inner bore as the guidewire lumen in theregion of the ultrasound transducer, in the alternative to providing aseparate stand-off coaxially over another tubular member which forms theinner member, such as according to the FIG. 15D embodiment.

In a further mode, the elongate body (802) can also include additionallumens which lie either side by side to or coaxial with the guidewirelumen (804) and which terminate at ports located within the spacebetween the inner member (803) and the transducer (830). A coolingmedium can circulate through space defined by the stand-off (838)between the inner member (803) and the transducer (830) via theseadditional lumens. By way of example, carbon dioxide gas, circulated ata rate of 5 liters per minute, can be used as a suitable cooling mediumto maintain the transducer at a lower operating temperature. It isbelieved that such thermal cooling would allow more acoustic power totransmit to the targeted tissue without degradation of the transducermaterial.

The transducer (830) desirably is electrically and mechanically isolatedfrom the interior of the balloon (820). Again, any of a variety ofcoatings, sheaths, sealants, tubings and the like may be suitable forthis purpose, such as those described in U.S. Pat. Nos. 5,620,479 and5,606,974. In the illustrated embodiment, as best illustrated in FIG.15C, a conventional, flexible, acoustically compatible, and medicalgrade epoxy (842) is applied over the transducer (830). The epoxy (842)may be, for example, Epotek 301, Epotek 310, which is availablecommercially from Epoxy Technology, or Tracon FDA-8. In addition, aconventional sealant, such as, for example, General Electric Silicon IIgasket glue and sealant, desirably is applied at the proximal and distalends of the transducer (830) around the exposed portions of the innermember (803), wires (836, 837) and stand-off (838) to seal the spacebetween the transducer (830) and the inner member (803) at theselocations.

An ultra thin-walled polyester heat shrink tubing (844) or the like thenseals the epoxy coated transducer. Alternatively, the epoxy coveredtransducer (830), inner member (803) and stand-off (838) can be insteadinserted into a tight thin wall rubber or plastic tubing made from amaterial such as Teflon®, polyethylene, polyurethane, silastic or thelike. The tubing desirably has a thickness of 0.0005 to 0.003 inches.

When assembling the ablation device assembly, additional epoxy isinjected into the tubing after the tubing is placed over the epoxycoated transducer (830). As the tube shrinks, excess epoxy flows out anda thin layer of epoxy remains between the transducer and the heat shrinktubing (844). These layers (842, 844) protect the transducer surface,help acoustically match the transducer (830) to the load, makes theablation device more robust, and ensures air-tight integrity of the airbacking.

Although not illustrated in FIG. 15A in order to simplify the drawing,the tubing (844) extends beyond the ends of transducer (830) andsurrounds a portion of the inner member (803) on either side of thetransducer (830). A filler (not shown) can also be used to support theends of the tubing (844). Suitable fillers include flexible materialssuch as, for example, but without limitation, epoxy, Teflon® tape andthe like.

The ultrasonic actuator (840) generates alternating current to power thetransducer (830). The ultrasonic actuator (840) drives the transducer(830) at frequencies within the range of about 5 to about 20 MHz, andpreferably for the illustrated application within the range of about 7MHz to about 10 MHz. In addition, the ultrasonic driver can modulate thedriving frequencies and/or vary power in order to smooth or unify theproduced collimated ultrasonic beam. For instance, the functiongenerator of the ultrasonic actuator (840) can drive the transducer atfrequencies within the range of 6.8 MHz and 7.2 MHz by continuously ordiscretely sweeping between these frequencies.

The ultrasound transducer (830) of the present embodiment sonicallycouples with the outer skin of the balloon (820) in a manner which formsa circumferential conduction block in a pulmonary vein as follows.Initially, the ultrasound transducer is believed to emit its energy in acircumferential pattern which is highly collimated along thetransducer's length relative to its longitudinal axis L (see FIG. 15D).The circumferential band therefore maintains its width andcircumferential pattern over an appreciable range of diameters away fromthe source at the transducer. Also, the balloon is preferably inflatedwith fluid which is relatively ultrasonically transparent, such as, forexample, degassed water. Therefore, by actuating the transducer (830)while the balloon (820) is inflated, the circumferential band of energyis allowed to translate through the inflation fluid and ultimatelysonically couple with a circumferential band of balloon skin whichcircumscribes the balloon (820). Moreover, the circumferential band ofballoon skin material may also be further engaged along acircumferential path of tissue which circumscribes the balloon, such as,for example, if the balloon is inflated within and engages a pulmonaryvein wall, ostium, or region of atrial wall. Accordingly, where theballoon is constructed of a relatively ultrasonically transparentmaterial, the circumferential band of ultrasound energy is allowed topass through the balloon skin and into the engaged circumferential pathof tissue such that the circumferential path of tissue is ablated.

Further to the transducer-balloon relationship just described, theenergy is coupled to the tissue largely via the inflation fluid andballoon skin. It is believed that, for in vivo uses of the presentinvention, the efficiency of energy coupling to the tissue, andtherefore ablation efficiency, may significantly diminish incircumstances where there is poor contact and conforming interfacebetween the balloon skin and the tissue. Accordingly, it is contemplatedthat several different balloon types may be provided for ablatingdifferent tissue structures so that a particular shape may be chosen fora particular region of tissue to be ablated.

In one particular balloon-transducer combination shown in FIG. 15C andalso in FIG. 16A, the ultrasound transducer preferably has a length suchthat the ultrasonically coupled band of the balloon skin, having asimilar length d according to the collimated electrical signal, isshorter than the working length D of the balloon. According to thisaspect of the relationship, the transducer is adapted as acircumferential ablation member which is coupled to the balloon to forman ablation element along a circumferential band of the balloon,therefore forming a circumferential ablation element band whichcircumscribes the balloon. Preferably, the transducer has a length whichis less than two-thirds the working length of the balloon, and morepreferably is less than one-half the working length of the balloon. Bysizing the ultrasonic transducer length d smaller than the workinglength D of the balloon (820)—and hence shorter than a longitudinallength of the engagement area between the balloon (820) and the wall ofthe body space (e.g., pulmonary vein ostium)—and by generally centeringthe transducer (830) within the balloon's working length D, thetransducer (830) operates in a field isolated from the blood pool. Agenerally equatorial position of the transducer (830) relative to theends of the balloon's working length also assists in the isolation ofthe transducer (830) from the blood pool.

It is believed that the transducer placement according to thisarrangement may be preventative of thrombus formation which mightotherwise occur at a lesion sight, particularly in the left atrium.

The ultrasound transducer described in various levels of detail abovehas been observed to provide a suitable degree of radiopacity forlocating the energy source at a desired location for ablating theconductive block. However, it is further contemplated that the elongatebody (802) may include an additional radiopaque marker or markers (notshown) to identify the location of the ultrasonic transducer (830) inorder to facilitate placement of the transducer at a selected ablationregion of a pulmonary vein via X-ray visualization. The radiopaquemarker is opaque under X-ray, and can be constructed, for example, of aradiopaque metal such as gold, platinum, or tungsten, or can comprise aradiopaque polymer such as a metal loaded polymer. The radiopaque markeris positioned coaxially over an inner tubular member (803), in a mannersimilar to that described in connection with the embodiment of FIG. 12.

The present circumferential ablation device is introduced into apulmonary vein of the left atrium in a manner similar to that describedabove. Once properly positioned within the pulmonary vein or veinostium, the pressurized fluid source inflates the balloon (820) toengage the lumenal surface of the pulmonary vein ostium. Once properlypositioned, the ultrasonic driver (840) is energized to drive thetransducer (830). It is believed that by driving the ultrasonictransducer 830 at 20 acoustical watts at an operating frequency of 7megahertz, that a sufficiently sized lesion can be formedcircumferentially about the pulmonary vein ostium in a relatively shortperiod of time (e.g., 1 to 2 minutes or less). It is also contemplatedthat the control level of energy can be delivered, then tested forlesion formation with a test stimulus in the pulmonary vein, either froman electrode provided at the tip area of the ultrasonic catheter or on aseparate device such as a guidewire through the ultrasonic catheter.Therefore, the procedure may involve ablation at a first energy level intime, then check for the effective conductive block provided by theresulting lesion, and then subsequent ablations and testing until acomplete conductive block is formed. In the alternative, thecircumferential ablation device may also include feedback control, forexample, if thermocouples are provided at the circumferential elementformed along the balloon outer surface. Monitoring temperature at thislocation provides indicia for the progression of the lesion. Thisfeedback feature may be used in addition to or in the alternative to themulti-step procedure described above.

FIGS. 16A-C show various alternative embodiments of the presentinvention for the purpose of illustrating the relationship between theultrasound transducer and balloon of the present invention justdescribed above. More specifically, FIG. 16A shows the balloon (820)having “straight” configuration with a working length D and a relativelyconstant diameter X between proximal and distal tapers (824, 826). As isshown in FIG. 16A, this variation is believed to be particularly welladapted for use in forming a circumferential conduction block along acircumferential path of tissue which circumscribes and transects apulmonary vein wall. However, unless the balloon is constructed of amaterial having a high degree of compliance and conformability, thisshape may provide for gaps in contact between the desiredcircumferential band of tissue and the circumferential band of theballoon skin along the working length of the balloon (820).

The balloon (820) in FIG. 16A is also concentrically positioned relativeto the longitudinal axis of the elongate body (802). It is understood,however, that the balloon can be asymmetrically positioned on theelongate body, and that the ablation device can include more than oneballoon.

FIG. 16B shows another assembly according to the invention, althoughthis assembly includes a balloon (820) which has a tapered outerdiameter from a proximal outer diameter X₁ to a smaller distal outerdiameter X₂. (Like reference numerals have been used in each of theseembodiments in order to identify generally common elements between theembodiments.) According to this mode, this tapered shape is believed toconform well to other tapering regions of space, and may also beparticularly beneficial for use in engaging and ablating circumferentialpaths of tissue along a pulmonary vein ostium.

FIG. 16C further shows a similar shape for the balloon as that justillustrated by reference to FIG. 16B, except that the FIG. 16Cembodiment further includes a balloon (820) and includes a bulbousproximal end (846). In the illustrated embodiment, the proximate bulbousend (846) of the central region (822) gives the balloon (820) a“pear”-shape. More specifically, a contoured surface (848) is positionedalong the tapered working length L and between proximal shoulder (824)and the smaller distal shoulder (826) of balloon (820). As is suggestedby view of FIG. 16C, this pear shaped embodiment is believed to bebeneficial for forming the circumferential conduction block along acircumferential path of atrial wall tissue which surrounds and perhapsincludes the pulmonary vein ostium. For example, the device shown inFIG. 16C is believed to be suited to form a similar lesion to that shownat circumferential lesion (850) in FIG. 16D. Circumferential lesion(850) electrically isolates the respective pulmonary vein (852) from asubstantial portion of the left atrial wall. The device shown in FIG.16C is also believed to be suited to form an elongate lesion whichextends along a substantial portion of the pulmonary vein ostium (854),e.g., between the proximal edge of the illustrated lesion (850) and thedashed line (856) which schematically marks a distal edge of such anexemplary elongate lesion (850).

As mentioned above, the transducer (830) can be formed of an array ofmultiple transducer elements that are arranged in series and coaxial.The transducer can also be formed to have a plurality of longitudinalsectors. These modes of the transducer have particular utility inconnection with the tapering balloon designs illustrated in FIGS. 16Band 16C. In these cases, because of the differing distances along thelength of the transducer between the transducer and the targeted tissue,it is believed that a non-uniform heating depth could occur if thetransducer were driven at a constant power. In order to uniformly heatthe targeted tissue along the length of the transducer assembly, morepower may therefore be required at the proximal end than at the distalend because power falls off as 1/radius from a source (i.e., from thetransducer) in water. Moreover, if the transducer (830) is operating inan attenuating fluid, then the desired power level may need to accountfor the attenuation caused by the fluid. The region of smaller balloondiameter near the distal end thus requires less transducer power outputthan the region of larger balloon diameter near the proximal end.Further to this premise, in a more specific embodiment transducerelements or sectors, which are individually powered, can be provided andproduce a tapering ultrasound power deposition. That is, the proximaltransducer element or sector can be driven at a higher power level thanthe distal transducer element or sector so as to enhance the uniformityof heating when the transducer lies skewed relative to the target site.

The circumferential ablation device (800) can also include additionalmechanisms to control the depth of heating. For instance, the elongatebody (802) can include an additional lumen which is arranged on the bodyso as to circulate the inflation fluid through a closed system. A heatexchanger can remove heat from the inflation fluid and the flow ratethrough the closed system can be controlled to regulate the temperatureof the inflation fluid. The cooled inflation fluid within the balloon(820) can thus act as a heat sink to conduct away some of the heat fromthe targeted tissue and maintain the tissue below a desired temperature(e.g., 90 decrees C.), and thereby increase the depth of heating. Thatis, by maintaining the temperature of the tissue at the balloon/tissueinterface below a desired temperature, more power can be deposited inthe tissue for greater penetration. Conversely, the fluid can be allowedto warm. This use of this feature and the temperature of the inflationfluid can be varied from procedure to procedure, as well as during aparticular procedure, in order to tailor the degree of ablation to agiven application or patient.

The depth of heating can also be controlled by selecting the inflationmaterial to have certain absorption characteristics. For example, byselecting an inflation material with higher absorption than water, lessenergy will reach the balloon wall, thereby limiting thermal penetrationinto the tissue. It is believed that the following fluids may besuitable for this application: vegetable oil, silicone oil and the like.

Uniform heating can also be enhanced by rotating the transducer withinthe balloon. For this purpose, the transducer (830) may be mounted on atorquible member which is movably engaged within a lumen that is formedby the elongate body (802).

Another aspect of the balloon-transducer relationship of the presentembodiment is also illustrated by reference to FIGS. 17A-B. In generalas to the variations embodied by those figures, the circumferentialultrasound energy signal is modified at the balloon coupling level suchthat a third order of control is provided for the tissue lesion pattern(the first order of control is the transducer properties affectingsignal emission, such as length, width, shape of the transducer crystal;the second order of control for tissue lesion pattern is the balloonshape, per above by reference to FIGS. 16A-C).

More particularly, FIG. 17A shows balloon (820) to include a filter(860) which has a predetermined pattern along the balloon surface andwhich is adapted to shield tissue from the ultrasound signal, forexample, by either absorbing or reflecting the ultrasound signal. In theparticular variation shown in FIG. 17A, the filter (860) is patterned sothat the energy band which is passed through the balloon wall issubstantially more narrow than the band which emits from the transducer(830) internally of the balloon (820). The filter (860) can beconstructed, for example, by coating the balloon (820) with anultrasonically reflective material, such as with a metal, or with anultrasonically absorbent material, such as with a polyurathaneelastomer. Or, the filter (860) can be formed by varying the balloon'swall thickness such that a circumferential band (862), which is narrowin the longitudinal direction as compared to the length of the balloon,is also thinner (in a radial direction) than the surrounding regions,thereby preferentially allowing signals to pass through the band (862).The thicker walls of the balloon (820) on either side of the band (862)inhibit propagation of the ultrasonic energy through the balloon skin atthese locations.

For various reasons, the “narrow pass filter” embodiment of FIG. 17A maybe particularly well suited for use in forming circumferentialconduction blocks in left atrial wall and pulmonary vein tissuesaccording to the present invention. It is believed that the efficiencyof ultrasound transmission from a piezoelectric transducer is limited bythe length of the transducer, which limitations are further believed tobe a function of the wavelength of the emitted signal. Thus, for someapplications a transducer (830) may be required to be longer than thelength which is desired for the lesion to be formed. Many proceduresintending to form conduction blocks in the left atrium or pulmonaryveins, such as, for example, less-invasive “maze”-type procedures,require only enough lesion width to create a functional electrical blockand to electrically isolate a tissue region. In addition, limiting theamount of damage formed along an atrial wall, even in a controlledablation procedure, pervades as a general concern. However, a transducerthat is necessary to form that block, or which may be desirable forother reasons, may require a length which is much longer and may createlesions which are much wider than is functionally required for theblock. A “narrow pass” filter along the balloon provides one solution tosuch competing interests.

FIG. 17B shows another variation of the balloon-transducer relationshipin an ultrasound ablation assembly according to the present invention.Unlike the variation shown in FIG. 17A, FIG. 17B shows placement of anultrasonically absorbent band (864) along balloon (820) and directly inthe central region of the emitted energy signal from transducer (830).According to this variation, the ultrasonically absorbent band (864) isadapted to heat to a significant temperature rise when sonically coupledto the transducer via the ultrasound signal. It is believed that someablation methods may benefit from combining ultrasound/thermalconduction modes of ablation in a targeted circumferential band oftissue. In another aspect of this variation, ultrasonically absorbentband (864) may operate as an energy sink as an aid to control the extentof ablation to a less traumatic and invasive level than would be reachedby allowing the raw ultrasound energy to couple directly to the tissue.In other words, by heating the absorbent band (864) the signal isdiminished to a level that might have a more controlled depth of tissueablation. Further to this aspect; absorbent band (864) may thereforealso have a width which is more commensurate with the length of thetransducer, as is shown in an alternative mode in shadow at absorbentband (864).

In each of the embodiments illustrated in FIGS. 15A through 17B, theultrasonic transducer had an annular shape so as to emit ultrasonicenergy around the entire circumference of the balloon. The presentcircumferential ablation device, however, can emit a collimated beam ofultrasonic energy in a specific angular exposure. For instance, as seenin FIG. 18A, the transducer can be configured to have only a singleactive sector (e.g., 180 degree exposure). The transducer can also havea planar shape. By rotating the elongate body (802), the transducer(830) can be swept through 360 degrees in order to form acircumferential ablation. For this purpose, the transducer (830) may bemounted on a torquible member (803), in the manner described above.

FIG. 18B illustrates another type of ultrasonic transducer which can bemounted to a torquible member (803) within the balloon (820). Thetransducer (830) is formed by curvilinear section and is mounted on theinner member (803) with its concave surface facing in a radially outwarddirection. The inner member (803) desirably is formed with recess thatsubstantially matches a portion of the concave surface of the transducer(830). The inner member (803) also includes longitudinal ridges on theedges of the recess that support the transducer above the inner membersuch that an air gap is formed between the transducer and the innermember. In this manner, the transducer is “air-backed.” This spaced issealed and closed in the manner described above in connection with theembodiment of FIGS. 15A-E.

The inverted transducer section produces a highly directional beampattern. By sweeping the transducer through 360 degrees of rotation, asdescribed above, a circumferential lesion can be formed while using lesspower than would be required with a planar or tubular transducer.

It is to be further understood that the various modes of theultrasound-balloon embodiments just illustrated by reference to FIGS.15A-17B may be used according to several different particular methodssuch as those methods otherwise set forth throughout this disclosure.For example, any of the ultrasound transducer embodiments may be used toform a conduction block in order to prevent or treat focal arrhythmiaarising from a specific pulmonary vein, or may alternatively oradditionally be used for joining adjacent linear lesions in aless-invasive “maze”-type procedure.

While particular detailed description has been herein provided forparticular embodiments and variations according to the presentinvention, it is further understood that various modifications andimprovements may be made by one of ordinary skill according to thisdisclosure and without departing from the broad scope of the invention.

What is claimed is:
 1. A tissue ablation device assembly for ablating asubstantial portion of a circumferential region of tissue at a locationwhere a pulmonary vein extends from an atrium, comprising: an elongatebody with a proximal end portion and a distal end portion, the distalend portion having proximal and distal sections; an expandable memberincluding a proximal end and a distal end coupled to the proximal anddistal sections of the distal end portion, respectively, the expandablemember being adjustable between a radially collapsed condition and aradially expanded condition with an expanded outer diameter which isadapted to engage the substantial portion of the circumferential regionof tissue; and an ultrasound ablation element secured to the distalsection at a fixed position within the expandable member, wherein theultrasound ablation element is adapted to emit a substantiallycircumferential pattern of ultrasound energy and to ablatively couple tothe substantial portion of the circumferential region of tissue.
 2. Theassembly of claim 1, wherein the expanded outer diameter of theexpandable member is at least 1.0 centimeters when in the expandedcondition.
 3. The assembly of claim 1, wherein the expanded outerdiameter of the expandable member is at least 2.0 centimeters when inthe expanded condition.
 4. The assembly of claim 1, wherein the expandedouter diameter of the expandable member is between about 1.0 centimeterand about 2.5 centimeter when in the expanded condition.
 5. The assemblyof claim 1, wherein the distal end portion of the elongated bodycomprises a plurality of tubular members.
 6. The assembly of claim 1,wherein the ultrasound ablation element comprises a substantiallytubular ultrasound transducer that is mounted onto and surrounds thedistal end portion at the fixed position.
 7. The assembly of claim 6,wherein the distal end portion has an outer surface, and the ultrasoundtransducer is mounted onto the distal end portion with a radialseparation between at least a portion of the ultrasound transducer andthe outer surface of the distal end portion that forms a radialseparation region with a gas-filled gap.
 8. The assembly of claim 7,wherein the radial separation region is sealed to substantially preventfluid from entering from outside of the radial separation region intothe gap.
 9. The assembly of claim 7, further comprising a support memberbeing positioned within the radial separation region and bridgingbetween the distal end portion of the elongated body and the tubularultrasound transducer to thereby support at least in part the tubularultrasound transducer around the distal end portion of the elongatedbody.
 10. The assembly of claim 9, wherein the support member comprisesa substantially elastomeric material.
 11. The assembly of claim 7,wherein the distal end portion of the elongated body comprises aplurality of ridges that are spaced apart such that a plurality of saidradial separation regions is formed within the spaces between the ridgesand between tubular ultrasound transducer and the distal end portion.12. The assembly of claim 6, wherein the tubular ultrasound transducercomprises a piezoceramic material and has an electrically conductiveinner surface and an electrically conductive outer surface, and theassembly further comprising a first electrical lead with a distal endportion electrically coupled to the electrically conductive innersurface and a second electrical lead with a distal end portionelectrically coupled to the electrically conductive outer surface,wherein each of the first and second electrical leads also has aproximal end portion terminating along the proximal end portion of theelongate body, and wherein the proximal end portions of the electricalleads are adapted to couple to an electrical current source.
 13. Theassembly of claim 1, wherein the ultrasound ablation element comprisesan array of circumferentially spaced ultrasound transducer panels. 14.The assembly of claim 13, wherein each ultrasound transducer panel isadapted to be individually actuated, such that each ultrasoundtransducer panel is adapted to be ablatively couple to the substantialportion of the circumferential region of tissue.
 15. The assembly ofclaim 14, wherein each of the circumferentially spaced ultrasoundtransducer panels in the array comprises a piezoceramic material, andfurther comprising a plurality of actuating lead assemblies, each of theactuating lead assemblies being coupled to a corresponding one of theultrasound transducer panels in the array and also adapted to couple toan electrical current source.
 16. The assembly of claim 1, wherein theultrasound ablation element is adapted to ablatively couplesimultaneously to the substantial portion of the circumferential regionof tissue.
 17. The assembly of claim 1, wherein the ultrasound ablationelement is adapted to emit a continuous circumferential pattern ofultrasound energy whereby the entire circumferential region of tissue isablated.
 18. The assembly of claim 1, wherein the ultrasound ablationelement is adapted to emit an acoustic signal at a frequency of betweenabout 5 MHz to about 20 MHz.
 19. The assembly of claim 1, wherein theultrasound ablation element is adapted to emit an acoustic signal at apower level of at least about 20 Watts per centimeter radiator.
 20. Theassembly of claim 1, wherein the elongate body further comprises atracking member that is adapted to slideably engage and track over aguide member positioned within the pulmonary vein.
 21. The assembly ofclaim 1, further comprising at least one or more electrodes locatedalong the distal end portion of the elongated body and disposed so as tocontact tissue, said electrodes adapted to deliver and/or senseelectrical signals to and from the tissue.